Anti-5T4 antibodies and uses thereof

ABSTRACT

Anti-5T4 antibodies, anti-5T4 antibody/drug conjugates, and methods for preparing and using the same.

RELATED APPLICATIONS

Priority is claimed to U.S. Provisional Application No. 60/891,248,filed Feb. 23, 2007, and to U.S. Provisional Application No. 60/781,346,filed Mar. 10, 2006, each of which is incorporated by reference in itsentirety herein.

FIELD OF THE INVENTION

The present invention generally relates to anti-5T4 antibodies andantibody/drug conjugates (i.e., immunoconjugates) for the diagnosisand/or treatment of neoplastic or malignant disorders. The presentinvention also relates to isolated variable region nucleic acids andpolypeptides for preparing anti-5T4 antibodies and antibody/drugconjugates.

BACKGROUND OF THE INVENTION

The availability of high affinity monoclonal antibodies has enabled thedevelopment of targeted immunotherapies. According to this approach, atherapeutic agent is coupled to an antibody with binding specificity fora defined target cell population. Therapeutic agents that have beenconjugated to monoclonal antibodies include cytotoxins, biologicalresponse modifiers, enzymes (e.g., ribonucleases), apoptosis-inducingproteins and peptides, and radioisotopes. Antibody/cytotoxin conjugatesare generally referred to as immunocytotoxins. Antibodies coupled tolow-molecular-weight drugs such as methothrexate are typically calledchemoantibody/drug conjugates. Conjugates described as immunomodulatorscontain biological response modifiers such as lymphokines, growthfactors, and complement-activating cobra venom factor (CVF).Radiolabeled antibodies include radioactive isotopes that may be usedfor radiotherapy as well as imaging.

Antibody-mediated drug delivery to tumor cells augments drug efficacy byminimizing its uptake in normal tissues. See e.g., Reff et al. (2002)Cancer Control 9:152-66; Sievers (2000) Cancer Chemother. Pharmacol. 46Suppl:S18-22; Goldenberg (2001) Crit. Rev. Oncol. Hematol. 39:195-201.MYLOTARG® (gemtuzumab ozogamicin) is a commercially available targetedimmunotherapy that works according to this principle and which isapproved for the treatment of acute myeloid leukemia in elderlypatients. See Sievers et al. (1999) Blood 93: 3678-84. In this case, thetargeting molecule is an anti-CD33 monoclonal antibody that isconjugated to calicheamicin.

Targeted immunotherapy in humans has nevertheless been limited, in partdue to adverse responses to non-human monoclonal antibodies. Earlyclinical trials using rodent antibodies revealed human anti-mouseantibody (HAMA) and human anti-rat antibody (HARA) responses, whichresult in rapid antibody clearance. Less immunogenic antibodies havesince been developed, including chimeric antibodies, humanizedantibodies, PRIMATIZED® antibodies, and human antibodies prepared usingtransgenic mice or phage display libraries. See Morrison et al. (1984)Proc. Natl. Acad. Sci. USA 81:6851-5; Queen et al. (1989) Proc. Natl.Acad. Sci. USA 86:10029-33; Newman et al. (1992) Biotechnology (NY)10:1455-60; Green et al. (1994) Nat. Genet. 7:13-21; Marks et al. (1991)J. Mol. Biol. 222:581-97. Avoidance of a HAMA response permits high doseand repeated dose administration to achieve a therapeutic response.

Candidate antibodies for drug targeting include antibodies thatrecognize oncofetal antigens, i.e., antigens present on fetal cells andneoplastic cells, and which are largely absent from normal adult cells.See e.g., Magdelenat (1992) J. Immunol. Methods 150: 133-43. The 5T4oncofetal antigen is a 72 kDa highly glycosylated transmembraneglycoprotein comprising a 42 kDa non-glycosylated core (Hole et al.(1988) Br. J. Cancer 57: 239-46, Hole et al. (1990) Int. J. Cancer 45:179-84; PCT International Publication No. WO89/07947; U.S. Pat. No.5,869,053). 5T4 includes an extracellular domain characterized by twoleucine-rich repeats (LRRs) and an intervening hydrophilic region, whichis an accessible site for targeted therapy (Myers et al. (1994) J. Biol.Chem. 269: 9319-24).

Human 5T4 is expressed in numerous cancer types, including carcinomas ofthe bladder, breast, cervix, endometrium, lung, esophagus, ovary,pancreas, stomach, and testes, and is substantially absent from normaltissues, except for syncytiotrophoblast in placenta (see, e.g., Southallet al. (1990) Br. J. Cancer 61: 89-95 (immunohistological distributionof 5T4 antigen in normal and malignant tissues); Mieke et al. (1997)Clin. Cancer Res. 3: 1923-1930 (low intercellular adhesion molecule 1and high 5T4 expression on tumor cells correlate with reduceddisease-free survival in colorectal carcinoma patients); Starzynska etal. (1994) Br. J. Cancer 69: 899-902 (prognostic significance of 5T4oncofetal antigen expression in colorectal carcinoma); Starzynska et al.(1992) Br. J. Cancer 66: 867-869 (expression of 5T4 antigen incolorectal and gastric carcinoma); Jones et al. (1990) Br. J. Cancer 61:96-100 (expression of 5T4 antigen in cervical cancer); Connor and Stern(199) Int. J. Cancer 46: 1029-1034 (loss of MHC class-I expression incervical carcinomas); Ali et al. (2001) Oral Oncology 37: 57-64 (patternof expression of the 5T4 oncofoetal antigen on normal, dysplastic andmalignant oral mucosa); PCT International Publication No. WO89/07947;U.S. Pat. No. 5,869,053). For example, tissues reported to have noexpression of 5T4 include the liver, skin, spleen, thymus, centralnervous system (CNS), adrenal gland, and ovary. Tissues reported to havefocal or low expression of 5T4 include the liver, skin, spleen, lymphnode, tonsil, thyroid, prostate, and seminal vesicles. Weak-moderatediffuse expression of 5T4 has been reported in the kidney, lung,pancreas, pharynx, and gastro-intestinal tract. The only tissue reportedto have high expression of 5T4 is syncytiotrophoblast; 5T4 was alsoabsent from normal serum or the serum of pregnant women (i.e., levels<10ng/ml). Overexpression of 5T4 in tumors has been correlated with diseaseprogression, and assessment of 5T4 expression has been suggested as auseful approach for identifying patients with short-term prognosis(Mulder et al. (1997) Clin. Cancer Res. 3: 1923-30, Naganuma et al.(2002) Anticancer Res. 22: 1033-1038, Starzynska et al. (1994) Br. J.Cancer 69: 899-902, Starzynska et al. (1998) Eur. J. Gastroenterol.Hepatol. 10: 479-484, Wrigley et al. (1995) Int. J. Gynecol. Cancer 5:269-274).

Several anti-5T4 antibodies have been described, including mAb5T4, alsocalled the H8 antibody, which recognizes a conformational epitope of the5T4 antigen (Shaw et al. (2002) Biochem. J. 363: 137-45, PCTInternational Publication No. WO98/55607), a rat monoclonal antibody(Woods et al. (2002) Biochem. J. 366: 353-65), and a mouse monoclonalantibody called 5T4 (U.S. Pat. No. 5,869,053). Single chain anti-5T4antibodies have also been described, as well as fusion proteins thatinclude anti-5T4 antibody sequences fused to a therapeutic molecule. Forexample, anti-5T4 antibody sequences fused to the human IgG1 constantdomain or to the extracellular domain of murine B7.1 induces cytolysisof 5T4-expressing tumor cell lines (Myers et al. (2002) Cancer GeneTher. 9: 884-896, Shaw et al. (2000) Biochim. Biophys. Acta. 1524:238-246; U.S. Patent Application Publication No. 2003/0018004).Similarly, a single chain anti-5T4 antibody fused to a superantigen maystimulate T cell-dependent cytolysis of non-small cell lung carcinomacells in vitro (Forsberg et al. (2001) Br. J. Cancer 85: 129-136). Aphase I clinical trial using PNU-214936, a murine Fab fragment of themonoclonal antibody 5T4 fused to a mutated superantigen staphylococcalenterocytotoxin A (SEA), showed limited toxicity and some anti-tumorresponse (Cheng et al. (2004) J. Clin. Oncol. 22(4):602-9). As analternate therapeutic approach, recombinant 5T4 vaccines are alsosuggested for the treatment of cancers (Mulryan et al. (2002) Mol.Cancer. Ther. 1: 1129-37; UK Patent Application Publication Nos.2,370,571 and 2,378,704; EP Patent Application Publication Nos. EP1,160,323 and 1,152,060).

The present invention provides novel anti-5T4 antibodies, anti-5T4/drugconjugates, methods for producing the disclosed antibodies andantibody/drug conjugates, and methods for their diagnostic andtherapeutic use.

SUMMARY OF THE INVENTION

The present invention provides novel anti-5T4 antibodies, conjugatesthereof, and methods for using the same. Also provided are isolatedanti-5T4 polypeptides and isolated nucleic acids encoding the same.

Anti-5T4 antibodies of the invention include antibodies thatspecifically bind human 5T4 antigen, wherein the antibody (a) comprisesan antigen binding domain of murine A1, A2, or A3 antibodies; (b)competes for 5T4 binding with murine A1, A2, or A3 antibodies; (c) bindsa 5T4 epitope bound by A1, A2, or A3 antibodies; or (d) comprises a5T4-binding fragment of an antibody of (a)-(c). The anti-5T4 antibodiesof the invention may be chimeric, humanized, single chain, an Fabfragment, a F(ab)2 fragment, a Fv fragment, tetrameric, tetravalent,multispecific, domain-specific, a single domain antibody, a fusionprotein, or a murine monoclonal. For example, humanized anti-5T4antibodies of the invention include antibodies comprising at least oneheavy chain variable region or at least one light chain variable region,wherein the humanized antibody or antibody fragment: (a) comprises anantigen binding domain of murine A1, A2, or A3 antibodies; (b) competesfor 5T4 binding with murine A1, A2, or A3 antibodies; (c) binds a 5T4epitope bound by A1, A2, or A3 antibodies; or (d) a 5T4-binding fragmentof an antibody of (a)-(c).

The anti-5T4 antibodies of the invention have a binding affinity forhuman 5T4 antigen of at least about 1×10⁻⁷ M to about 1×10⁻¹² M. Thedisclosed anti-5T4 antibodies and conjugates thereof may also showspecific binding by targeting of 5T4-expressing cells in vivo.

Representative anti-5T4 antibodies of the invention include antibodiescomprising a heavy chain variable region comprising (a) an amino acidsequence of residues 20-138 of SEQ ID NO:2; (b) an amino acid sequencethat is at least 85% identical to residues 20-138 of SEQ ID NO:2; (c) anamino acid sequence of residues 19-135 of SEQ ID NO:6; (d) an amino acidsequence that is at least 86% identical to residues 19-135 of SEQ IDNO:6; (e) an amino acid sequence of residues 20-141 of SEQ ID NO:10; (f)an amino acid sequence that is at least 91% identical to residues 20-141of SEQ ID NO:10; (g) an amino acid sequence of any one of SEQ ID NOs:49,51, 52, 54, 56, 77, 78, 81, or 82; (h) an amino acid sequence that is atleast 91% identical to SEQ ID NO:51; (i) an amino acid sequence that isat least 78% identical to SEQ ID NO:54; (j) an amino acid sequence thatis at least 89% identical to SEQ ID NO:77; (k) an amino acid sequencethat is at least 79% identical to SEQ ID NO:78; (l) an amino acidsequence that is at least 80% identical to SEQ ID NO:81; or (m) an aminoacid sequence that is at least 78% identical to SEQ ID NO:82.

Representative anti-5T4 antibodies of the invention include antibodiescomprising a light chain variable region comprising (a) an amino acidsequence of residues 21-127 of SEQ ID NO:4; (b) an amino acid sequencethat is at least 94% identical to residues 21-127 of SEQ ID NO:4; (c) anamino acid sequence of residues 23-130 of SEQ ID NO:8; (d) an amino acidsequence that is at least 96% identical to residues 23-130 of SEQ IDNO:8; (e) an amino acid sequence of residues 21-127 of SEQ ID NO:12; (f)an amino acid sequence that is at least 98% identical to residues 21-127of SEQ ID NO:12; (g) an amino acid sequence of any one of SEQ ID NOs:58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 79, 80, 83, or 84; (h) an aminoacid sequence that is at least 83% identical to SEQ ID NO:60; (i) anamino acid sequence that is at least 93% identical to SEQ ID NO:70; (j)an amino acid sequence that is at least 85% identical to SEQ ID NO:76;(k) an amino acid sequence that is at least 85% identical to SEQ IDNO:76; (l) an amino acid sequence that is at least 88% identical to SEQID NO:79; (m) an amino acid sequence that is at least 84% identical toSEQ ID NO:80; (n) an amino acid sequence that is at least 90% identicalto SEQ ID NO:83; or (o) an amino acid sequence that is at least 91%identical to SEQ ID NO:84.

For example, an anti-5T4 antibody can comprise (a) a heavy chainvariable region comprising an amino acid sequence of residues 20-138 ofSEQ ID NO:2, and a light chain variable region comprising an amino acidsequence of residues 21-127 of SEQ ID NO:4; (b) a heavy chain variableregion comprising an amino acid sequence derived from residues 19-135 ofSEQ ID NO:6, and a light chain variable region comprising an amino acidsequence derived from residues 23-130 of SEQ ID NO:8; or (c) a heavychain variable region comprising an amino acid sequence derived fromresidues 20-141 of SEQ ID NO:10, and a light chain variable regioncomprises an amino acid sequence derived from residues 21-127 of SEQ IDNO:12.

Chimeric and humanized anti-5T4 antibodies of the invention may compriseconstant regions derived from human constant regions, such as a humanlight chain constant region derived from human kappa light chainconstant region and a human heavy chain constant region derived from ahuman IgG1 or human IgG4 heavy chain constant region.

Representative humanized anti-5T4 antibodies of the invention includeantibodies comprising (a) framework regions comprising residues of ahuman antibody framework region; and (b) one or more CDRs of the lightchain variable region of SEQ ID NO:4, 8, or 12, or one or more CDRs ofthe heavy chain variable region of SEQ ID NO:2, 6, or 10. For example,residues of a human antibody framework region can comprise (a) a humanantibody light chain framework region of a DPK24 subgroup IV germ lineclone, a VκIII subgroup (DPK23, DPK22, DPK20, DPK21), or a VκI subgroupgerm line clone (DPK9, DPK1, O2, DPK7); (b) a human antibody heavy chainframework region selected from the group consisting of DP-21 (VH7),DP-54 (VH3-07), DP-47 (VH3-23), DP-53 (VH-74), DP-49 (VH3-30), DP-48(VH3-13), DP-75, DP-8(VH1-2), DP-25, V1-2b and VI-3 (VH1-03), DP-15 andV1-8 (VH1-08), DP-14 and V1-18 (VH1-18), DP-5 and V1-24P (VH1-24), DP-4(VH1-45), DP-7 (VH1-46), DP-10, DA-6 and YAC-7 (VH1-69), DP-88 (VH1-e),DP-3 and DA-8 (VH1-f); (c) a consensus sequence of a heavy chainframework region of (b); or (d) a framework region that is at least 63%identical to a framework region of (a)-(c).

Representative humanized anti-5T4 antibodies of the invention can alsoinclude two or more CDRs of SEQ ID NOs: SEQ ID NOs:2, 4, 6, 8, 10, or12, such as two or all three CDRs of the light chain variable region ofSEQ ID NO:4, 8, or 12, or two or all three CDRs of the heavy chainvariable region of SEQ ID NO:2, 6, or 10, or one or more CDRs or thelight chain variable region of SEQ ID NO:4, 8, or 12 and one or moreCDRs of the heavy chain variable region of SEQ ID NO:2, 6, or 12, or allof the CDRs or SEQ ID NOs: 2, 4, 6, 8, 10, or 12.

Representative chimeric and humanized anti-5T4 antibodies includeantibodies comprising a heavy chain variable region sequence comprising(a) an amino acid sequence of residues 20-138 of SEQ ID NO:2; (b) anamino acid sequence that is at least 85% identical to residues 20-138 ofSEQ ID NO:2; (c) an amino acid sequence of residues 19-135 of SEQ IDNO:6; (d) an amino acid sequence that is at least 86% identical toresidues 19-135 of SEQ ID NO:6; (e) an amino acid sequence of residues20-141 of SEQ ID NO:10; (f) an amino acid sequence that is at least 91%identical to residues 20-141 of SEQ ID NO:10; (g) an amino acid sequenceof residues 1-119 of SEQ ID NO:49; (h) an amino acid sequence that is atleast 90% identical to residues 1-119 of SEQ ID NO:49; or (i) an aminoacid sequence of a humanized heavy chain variable depicted in FIGS.9A-9C.

Additional chimeric and humanized anti-5T4 antibodies of the inventioninclude antibodies comprising a heavy chain variable region encoded by anucleic acid comprising (a) a nucleotide sequence of nucleotides 58-414of SEQ ID NO:1; (b) a nucleotide sequence of nucleotides 55-405 of SEQID NO:5; (c) a nucleotide sequence of nucleotides 58-423 of SEQ ID NO:9;(d) a nucleotide sequence of nucleotides 1-358 of SEQ ID NO:48; (e) anucleotide sequence encoding a humanized A1, A2, or A3 variable regiondepicted in FIGS. 9A-9C; (f) a nucleotide sequence that is at least 90%identical to the nucleotide sequence of any one of (a)-(e); or (g) anucleic acid that specifically hybridizes to the complement of any oneof (a)-(e) under stringent hybridization conditions.

Representative chimeric and humanized anti-5T4 antibodies includeantibodies comprising a light chain variable region sequence comprising(a) an amino acid sequence of residues 21-127 of SEQ ID NO:4; (b) anamino acid sequence that is at least 94% identical to residues 21-127 ofSEQ ID NO:4; (c) an amino acid sequence of residues 23-130 of SEQ IDNO:8; (d) an amino acid sequence that is at least 96% identical toresidues 23-130 of SEQ ID NO:8; (e) an amino acid sequence of residues21-127 of SEQ ID NO:12; (f) an amino acid sequence that is at least 98%identical to residues 21-127 of SEQ ID NO:12; or (g) an amino acidsequence of a humanized A1, A2, or A3 light chain variable regiondepicted in FIGS. 9A-9C.

Also provided are antibody/drug conjugates for drug delivery comprising(a) a chimeric or humanized anti-5T4 antibody or antibody fragment ofthe invention; and (b) a drug, which is directly or indirectly bound tothe antibody. Representative drugs include therapeutic agents, such ascytotoxins, radioisotopes, immunomodulatory agents, anti-angiogenicagents, anti-proliferative agents, pro-apoptotic agents,chemotherapeutic agents, and therapeutic nucleic acids. A cytotoxin maybe, for example, an antibiotic, an inhibitor of tubulin polymerization,an alkylating agent, a protein synthesis inhibitor, a protein kinaseinhibitor, a phosphatase inhibitor, a topoisomerase inhibitor, or anenzyme. Antibiotic cytotoxins, such as calicheamicin,N-acetyl-γ-calicheamicin, or derivatives thereof such asN-acetyl-γ-calicheamicin dimethyl hydrazide, are particularly useful foranti-cancer therapies.

The disclosed anti-5T4 antibody/drug conjugates may include a linker forbinding the antibody to the drug. Representative linkers include4-(4′acetylphenoxy)butanoic acid (AcBut), 3-acetylphenyl acidic acid(AcPac), and 4-mercapto-4-methyl-pentanoic acid (Amide). Theantibody/drug conjugates may also include polyethylene glycol or otheragents to enhance drug incorporation.

For delivery of a drug to 5T4-expressing cells, the present inventionprovides methods whereby cells are contacted with an antibody/drugconjugate comprising (i) a chimeric or humanized anti-5T4 antibody, and(ii) a drug which is bound to the humanized anti-5T4 antibody directlyor indirectly. According to the disclosed methods, the drug isinternalized within the target cell. Therapeutic methods are alsodisclosed herein, which comprise administering to the subject having a5T4-positive cancer a therapeutically effective amount of an anti-5T4antibody/drug conjugate comprising (i) a chimeric or humanized anti-5T4antibody or antibody fragment, and (ii) a therapeutic agent which isbound to the humanized anti-5T4 antibody or antibody fragment directlyor indirectly. Anti-5T4 therapies of the invention may be combined withany other known therapy for improved effect. A second therapeutic agentmay be administered in combination with an anti-5T4 antibody/drugconjugate simultaneously or consecutively in any order.

Also provided are isolated nucleic acids encoding humanized anti-5T4variable regions, which are useful for production of the disclosedhumanized anti-5T4 antibodies. Representative nucleic acids encoding ahumanized anti-5T4 heavy chain variable region include (a) a nucleotidesequence of nucleotides 58-414 of SEQ ID NO:1; (b) a nucleotide sequenceof nucleotides 55-405 of SEQ ID NO:5; (c) a nucleotide sequence ofnucleotides 58-423 of SEQ ID NO:9; (d) a nucleotide sequence encodingany one of SEQ ID NOs:48, 50, 53, or 55; (e) a nucleotide sequence thatis 89% identical to SEQ ID NO:50 when the query coverage is 100%; (f) anucleotide sequence that is 82% identical to SEQ ID NO:53 when the querycoverage is 100%; or (g) a nucleic acid that specifically hybridizes tothe complement of any one of (a)-(d) under stringent hybridizationconditions. Representative nucleic acids encoding a humanized anti-5T4light chain variable region include (a) a nucleotide sequence ofnucleotides 61-381 of SEQ ID NO:3; (b) a nucleotide sequence ofnucleotides 67-390 of SEQ ID NO:7; (c) a nucleotide sequence ofnucleotides 61-381 of SEQ ID NO:11; (d) a nucleotide sequence encoding ahumanized A1, A2, or A3 light chain variable region of any one of SEQ IDNOs: 57, 59, 61, 63, 65, 67, 69, 71, 73, or 75; (e) a nucleotidesequence that is 84% identical to SEQ ID NO:59 when the query coverageis 100%; (f) a nucleotide sequence that is 86% identical to SEQ ID NO:69when the query coverage is 100%; (g) a nucleotide sequence that is 85%identical to SEQ ID NO:75 when the query coverage is 100%; or (h) anucleic acid that specifically hybridizes to the complement of any oneof (a)-(d) under stringent hybridization conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show the nucleotide and amino acid sequences of the heavychain and light chain variable regions of murine anti-5T4 antibodies A1,A2, and A3. The amino acid sequences are annotated to identifycomplementarity determining regions (CDRs) by underlining and the leadersequence by double-underlining.

FIG. 2 is a Western blot prepared using CT26/5T4 cell lysates and probedwith the indicated antibodies.

FIGS. 3A-3B are line graphs that show response curves and bindingkinetics for two independent preparations of H8 and A1 antibodies. Thepreparations were substantially equivalent.

FIGS. 4A-4C are line graphs that show modulation of H8, A1, A2, and A3antibodies by MDAMB435/5T4 cells. Levels of antibody at the cell surfacedecline over time (FIGS. 4A, 4C (solid)), while the levels of antibodyin the supernatant remain constant (FIGS. 4B, 4C (open)). MCF, meancellular fluorescence; supt, supernatant.

FIG. 5 is a schematic diagram of the human ectodomain 5T4 Fc construct,the mouse ectodomain 5T4 Fc construct, and the human/mouse 5T4 chimeraconstructs. These constructs were used for epitope mapping as describedin Example 4

FIGS. 6A-6B show graphical results of competitive binding of humanizedH8 and each of the indicated antibodies to human 5T4 ectodomain Fcfusion protein. HuH8, humanized H8 antibody; ChiA1, chimeric A1antibody; ChiA1+C67F, chimeric A1 antibody bearing C67F mutation; ChiA2,chimeric A2 antibody; muA2, murine A2 antibody; ChiA3, chimeric A3antibody; ChiA3+C91Y, chimeric A3 antibody bearing C91Y mutation, muA3,murine A3 antibody; No Ab, no antibody (control).

FIG. 7 is a linear diagram showing the human 5T4 epitopes bound by H8,A1, A2, and A3. The indicated residues are residues of the 5T4 antigendescribed by Myers et al. (1994) J. Biol. Chem. 269(12):9319-9324, alsoavailable as GenBank Accession No. Z29083 (SEQ ID NO:87). LRR,Leucine-rich repeat.

FIG. 8 shows the results of spheroid assays performed as described inExample 6. Anti-5T4/calicheamicin conjugates prepared using the A1 andA3 antibodies significantly inhibited growth of 5T4-expressing cells(MDAMB435/5T4) as compared to control cells (MDAMB435/neo). CMA-676,anti-CD33/calicheamicin conjugate; huH8-AcBut-CalichDMH, humanized H8antibody conjugated to calicheamicin using 4-(4′-acetylphenoxy)butanoicacid (AcBut); CalichDMH, unconjugated calicheamicin; A1-AcBut-CalichDMH,A1 antibody conjugated to calicheamicin using4-(4′-acetylphenoxy)butanoic acid (AcBut); A3-AcBut-CalichDMH, A3antibody conjugated to calicheamicin using 4-(4′-acetylphenoxy)butanoicacid (AcBut).

FIGS. 9A-9H show nucleotide and amino acid sequences of the humanized A1heavy chain variable region version 1 (SEQ ID NOs:48-49); amino acidsequences of humanized A1 heavy chain variable region (huA1 VH) versions1.2 and 2.0; amino acid sequences of humanized A1 light chain variableregion (huA1 VL) versions 1.0, 2.0, and 3.0; amino acid sequences ofhumanized A2 heavy chain variable region versions 1.0 and 2.0 (huA2 VH);amino acid sequences of humanized A2 light chain variable regionversions 1.0 and 2.0 (huA2 VL); amino acid sequences of humanized A3heavy chain variable region versions 1.0 and 2.0 (huA3 VH); and aminoacid sequences of humanized A3 light chain variable region versions 1.0and 2.0 (huA32 VL). CDRs are underlined.

FIGS. 10A-10B show representative human heavy chain variable regionframework sequences that may be used to prepare humanized anti-5T4antibodies. FIG. 10A is an alignment of human heavy chain variableregion sequences of subgroup I (SEQ ID NOs:14-24) and the consensusframework sequences derived there from (SEQ ID NOs:25-27). FIG. 10Bshows the sequences of human germline genes of the VH 7 and VH 3subgroups (SEQ ID NOs:88-93).

FIG. 11 is an alignment of human light chain variable region sequencesof subgroup VκIII (SEQ ID NOs:29-34). Boxed sequences, CDRs.

FIG. 12 is an alignment of human light chain variable region sequencesof subgroup VκI (SEQ ID NOs:35-44). Boxed sequences, CDRs.

FIG. 13 shows additional human germline sequences of Vk 1 and Vk IVsubgroups, which have framework regions that may be used to preparehumanized anti-5T4 antibodies (SEQ ID NOs:94-99).

FIG. 14 shows the amino acid sequences of representative human constantregions that may be used to prepare chimeric and humanized anti-5T4antibodies (SEQ ID NOs:45-47).

FIG. 15 shows the amino acid sequences of a full-length cynomologousmonkey 5T4 antigen and a partial black-tailed marmoset 5T4 antigen.Underlined sequences, leader sequences. For each sequence, the 5T4ectodomain includes amino acids 30-356.

DETAILED DESCRIPTION OF THE INVENTION

I. Anti-5T4 Antibodies

The present invention provides novel murine antibodies that bind human5T4 antigen and that are useful for developing targeted immunotherapies.The human 5T4 antigen is a 72 kDa non-glycosylated phosphoprotein foundon the surface of trophoblast cells and numerous cancer cell types SeeHole et al. (1988) Br. J. Cancer 57: 239-46, Hole et al. (1990) Int. J.Cancer 45: 179-184; PCT International Publication No. WO89/07947; U.S.Pat. No. 5,869,053.

The murine anti-5T4 antibodies of the invention are designated A1, A2,and A3, and were prepared as described in Example 1. Also provided areanti-5T4 antibodies derived from A1, A2, and A3, and which specificallybind to human 5T4 antigen. For example, anti-5T4 antibodies of theinvention include antibodies comprising antigen binding residues fromthe A1, A2, and A3 antibodies; antibodies that compete for binding to5T4 antigen with A1, A2, or A3 antibodies; and antibodies that bind tothe same 5T4 epitope as A1, A2, or A3 antibodies.

In particular, the disclosed A1, A2, and A3 antibodies each comprise anantigen binding site that recognizes a unique epitope on the human 5T4antigen. Each of these antibodies also binds to an epitope distinct fromthat bound by H8, and each of A1, A2, and A3 fails to compete with theH8 antibody for binding to human 5T4. See Examples 4-5 and FIGS. 6-7.Accordingly, the present invention provides antibodies that specificallybind to residues 30-163 of human 5T4 (e.g., A3), antibodies thatspecifically bind to residues 224-276 of human 5T4 (e.g., A1), andantibodies that specifically bind to residues 224-355 of human 5T4(e.g., A2). Also provided are human 5T4 antigens comprising epitopesbound by an A1, A2, or A3 antibody. For example, the invention provides5T4 antigenic fragments comprising residues 30-163, 224-276, and 224-355of a native or full-length 5T4 antigen.

Specific binding of the disclosed anti-5T4 antibodies refers to apreferential binding of an antibody to human 5T4 antigen in aheterogeneous sample comprising multiple different antigens. Typically,specific binding occurs if the binding affinity is at least about 10⁻⁷ Mor higher, such as at least about 10⁻⁸ M or higher, including at leastabout 10⁻⁹ M or higher, at least about 10⁻¹¹ M or higher, or at leastabout 10⁻¹² M or higher. For example, specific binding of an antibody ofthe invention to a human 5T4 antigen includes binding in the range of atleast about 1×10⁻⁷ M to about 1×10⁻¹² M, such as within the range ofabout 1×10⁻⁸ M to about 1×10⁻¹² M, or within the range of about 1×10⁻⁸ Mto about 1×10⁻¹¹ M, or within the range of about 1×10⁻⁸ M to about1×10⁻¹⁰ M, or within the range of about 1×10⁻⁹ M to about 1×10⁻¹⁰ M.Specific binding also refers to selective targeting of an anti-5T4antibody to 5T4-expressing cells following administration of theantibody to a subject.

The anti-5T4 antibodies of the invention may have a tetrameric structure(e.g., similar to naturally occurring antibodies), or they may compriseany other structure having at least one immunoglobulin light chainvariable region or at least one immunoglobulin heavy chain region, or5T4-binding fragments thereof (e.g., Fab, modified Fab, F(ab′)₂ or Fvfragments. Also included are single domain antibodies, in which one ormore complementarity determining regions (CDRs), but less than all sixCDRs, constitute an antigen binding region. The invention alsoencompasses chimeric antibodies, humanized antibodies, superhumanizedantibodies, diabodies, single chain antibodies, tetravalent antibodies,and/or multispecific antibodies (e.g., bispecific antibodies). Theseantibody descriptors are not mutually exclusive.

Naturally occurring antibodies are tetrameric (H₂L₂) glycoproteins ofabout 150,000 daltons, composed of two identical light (L) chains andtwo identical heavy (H) chains. The two heavy chains are linked to eachother by disulfide bonds and each heavy chain is linked to a light chainby a disulfide bond. Each of the light and heavy chains is furthercharacterized by an amino-terminal variable region and a constantregion. The variable regions include sequences that differ extensivelyamong antibodies and substantially determine the binding affinity andspecificity of a particular antibody for its particular antigen. Thevariable regions of each of the light and heavy chains align to form theantigen-binding domain.

Chimeric antibodies comprise sequences from at least two differentspecies. As one example, recombinant cloning techniques may be used toinclude variable regions, which contain the antigen-binding sites, froma non-human antibody (i.e., an antibody prepared in a non-human speciesimmunized with the antigen) and constant regions derived from a humanimmunoglobulin.

Chimeric anti-5T4 antibodies of the invention include antibodiescomprising heavy chain and light chain variable regions of the A1, A2,and A3 antibodies, i.e., (a) a heavy chain variable region having anamino acid sequence of residues 20-138 of SEQ ID NO:2 and a light chainvariable region having an amino acid sequence of residues 21-127 of SEQID NO:4; (b) a heavy chain amino acid sequence of residues 19-135 of SEQID NO:6 and a light chain amino acid sequence of residues 23-130 of SEQID NO:8; and (c) a heavy chain amino acid sequence of residues 20-141 ofSEQ ID NO:10 and a light chain amino acid sequence of residues 21-127 ofSEQ ID NO:12. Representative humanized anti-5T4 antibodies may include aheavy chain variable region set for as amino acids 1-119 of SEQ IDNO:49, or any one of the humanized heavy chain variable region depictedin FIGS. 9A-9C, and a humanized light chain variable region, alsodepicted in FIGS. 9A-9C. Preparation of representative chimeric andhumanized anti-5T4 antibodies of the invention is described in Example7.

Anti-5T4 antibodies of the invention may also comprise a heavy chainand/or light chain variable region comprising an amino acid sequencethat is derived from or substantially similar to the A1, A2, or A3variable regions, or substantially similar to the humanized A1, A2, andA3 variable regions. With respect to substantially identical heavy chainand light chain variable regions, the substantially identical sequencesare at least about 90% identical to the variable region sequences of anyone of SEQ ID NOs:1-12 or to the humanized A1, A2, and A3 variableregions depicted in FIGS. 9A-9C, such as at least 91% identical, or atleast 92% identical, or at least 93% identical, or at least 94%identical, or at least 95% identical, or at least 96% identical, or atleast 97% identical, or at least 98% identical, or at least 99%identical.

Representative chimeric anti-5T4 antibodies of the invention, i.e.,antibodies that specifically bind to 5T4 antigen, also include thoseantibodies having (a) a heavy chain variable region amino acid sequenceset forth as residues 20-138 of SEQ ID NO:2, residues 19-135 of SEQ IDNO:6, residues 20-141 of SEQ ID NO:10, or any one of the humanized A1,A2, or A3 heavy chain variable regions depicted in FIGS. 9A-9C; (b) aheavy chain variable region amino acid sequence that is at least 85%identical to residues 20-138 of SEQ ID NO:2; (c) a heavy chain variableregion amino acid sequence that is at least 86% identical to residues19-135 of SEQ ID NO:6; (d) a heavy chain variable region amino acidsequence that is at least 91% identical to residues 20-141 of SEQ IDNO:10; (e) a heavy chain variable region amino acid sequence that is atleast 90% identical to residues 1-119 of SEQ ID NO:49; or (f) a heavychain variable region amino acid sequence derived from any one of thehumanized A1, A2, or A3 variable regions depicted in FIGS. 9A-9C.

A heavy chain variable region of a chimeric or humanized anti-5T4antibody, which specifically binds to 5T4 antigen, may be encoded by (a)a nucleic acid comprising a nucleotide sequence of nucleotides 58-414 ofSEQ ID NO:1, nucleotides 55-405 of SEQ ID NO:5, nucleotides 58-423 ofSEQ ID NO:9, nucleotides 1-358 of SEQ ID NO:48; or a nucleic acidencoding a humanized A1, A2, or A3 heavy chain variable region depictedin FIGS. 9A-9C; (b) a nucleic acid comprising a nucleotide sequence thatis at least 90% identical to a nucleic acid comprising a nucleotidesequence of nucleotides 58-414 of SEQ ID NO:1, nucleotides 55-405 of SEQID NO:5, or nucleotides 58-423 of SEQ ID NO:9. For example, a heavychain variable region of a chimeric anti-5T4 antibody may be encoded bya nucleic acid that is at least 98% identical to nucleotides 58-414 ofSEQ ID NO:1, a nucleic acid comprising a nucleotide sequence that is atleast 98% identical to nucleotides 55-405 of SEQ ID NO:5, or a nucleicacid comprising a nucleotide sequence that is at least 89% identical tonucleotides 1-358 of SEQ ID NO:48. A heavy chain variable region of achimeric anti-5T4 antibody may also be encoded by a nucleic acid thatspecifically hybridizes to the complement of a nucleic acid comprising anucleotide sequence of nucleotides 58-414 of SEQ ID NO:1, nucleotides55-405 of SEQ ID NO:5, nucleotides 58-423 of SEQ ID NO:9, or nucleotides1-358 of SEQ ID NO:48, under stringent hybridization conditions, forexample final wash conditions of 0.1×SSC at 65° C.

Representative chimeric anti-5T4 antibodies of the invention furtherinclude those antibodies having (a) a light chain variable region aminoacid sequence set forth as residues 21-127 of SEQ ID NO:4, residues23-130 of SEQ ID NO:8, residues 21-127 of SEQ ID NO:12, or residues of ahumanized A1, A2, or A3 light chain variable region depicted in FIGS.9A-9C; or (b) a light chain variable region amino acid sequence that isat least 90% identical to residues 21-127 of SEQ ID NO:4, residues23-130 of SEQ ID NO:8, or residues 21-127 of SEQ ID NO:12. For example,a light chain variable region amino acid sequence may comprise (a) alight chain variable region amino acid sequence that is at least 94%identical to residues 21-127 of SEQ ID NO:4; (b) a light chain variableregion amino acid sequence that is at least 96% identical to residues23-130 of SEQ ID NO:8; (c) a light chain variable region amino acidsequence that is at least 98% identical to residues 21-127 of SEQ IDNO:12; (d) or a light chain variable region amino acid sequence derivedfrom any one of the humanized A1, A2, or A3 light chain variable regionsdepicted in FIGS. 9A-9C.

A light chain variable region of a chimeric anti-5T4 antibody, whichspecifically binds to 5T4 antigen, may be encoded by (a) a nucleic acidcomprising a nucleotide sequence of nucleotides 61-381 of SEQ ID NO:3,nucleotides 67-390 of SEQ ID NO:7, nucleotides 61-381 of SEQ ID NO:11,or nucleotides encoding any one of the humanized A1, A2, or A3 lightchain variable regions depicted in FIGS. 9A-9C; or (b) a nucleic acidcomprising a nucleotide sequence that is at least 90% identical tonucleotides 61-381 of SEQ ID NO:3, nucleotides 67-390 of SEQ ID NO:7, ornucleotides 61-381 of SEQ ID NO:11. For example, a light chain variableregion of a chimeric anti-5T4 antibody may be encoded by a nucleic acidcomprising (a) a nucleotide sequence that is at least 97% identical tonucleotides 61-381 of SEQ ID NO:3; (b) a nucleotide sequence that is atleast 98% identical to nucleotides 67-390 of SEQ ID NO:7; or (c) anucleotide sequence that is at least 99% identical to nucleotides 61-381of SEQ ID NO:11. A light chain variable region of a chimeric anti-5T4antibody, which specifically binds to 5T4 antigen, may also be encodedby a nucleic acid that specifically hybridizes to the complement of anucleic acid comprising a nucleotide sequence of nucleotides 61-381 ofSEQ ID NO:3, nucleotides 67-390 of SEQ ID NO:7, or nucleotides 61-381 ofSEQ ID NO:11, under stringent hybridization conditions, for examplefinal wash conditions of 0.1×SSC at 65° C.

Humanized antibodies are a type of chimeric antibody wherein variableregion residues responsible for antigen binding (i.e., residues of acomplementarity determining region, abbreviated complementaritydetermining region, or any other residues that participate in antigenbinding) are derived from a non-human species, while the remainingvariable region residues (i.e., residues of the framework regions) andconstant regions are derived, at least in part, from human antibodysequences. A subset of framework region residues and constant regionresidues of a humanized antibody may be derived from non-human sources.Variable regions of a humanized antibody are also described as humanized(i.e., a humanized light or heavy chain variable region). The non-humanspecies is typically that used for immunization with antigen, such asmouse, rat, rabbit, non-human primate, or other non-human mammalianspecies. Humanized antibodies are typically less immunogenic thantraditional chimeric antibodies and show improved stability followingadministration to humans. See e.g., Benincosa et al. (2000) J.Pharmacol. Exp. Ther. 292:810-6; Kalofonos et al. (1994) Eur. J. Cancer30A:1842-50; Subramanian et al. (1998) Pediatr. Infect. Dis. J.17:110-5.

Complementarity determining regions (CDRs) are residues of antibodyvariable regions that participate in antigen binding. Several numberingsystems for identifying CDRs are in common use. The Kabat definition isbased on sequence variability, and the Chothia definition is based onthe location of the structural loop regions. The AbM definition is acompromise between the Kabat and Chothia approaches. The CDRs of thelight chain variable region are bounded by the residues at positions 24and 34 (CDR1-L), 50 and 56 (CDR2-L), and 89 and 97 (CDR3-L) according tothe Kabat, Chothia, or AbM algorithm. According to the Kabat definition,the CDRs of the heavy chain variable region are bounded by the residuesat positions 31 and 35B (CDR1-H), 50 and 65 (CDR2-H), and 95 and 102(CDR3-H) (numbering according to Kabat). According to the Chothiadefinition, the CDRs of the heavy chain variable region are bounded bythe residues at positions 26 and 32 (CDR1-H), 52 and 56 (CDR2-H), and 95and 102 (CDR3-H) (numbering according to Chothia). According to the AbMdefinition, the CDRs of the heavy chain variable region are bounded bythe residues at positions 26 and 35B (CDR1-H), 50 and 58 (CDR2-H), and95 and 102 (CDR3-H) (numbering according to Kabat). See Martin et al.(1989) Proc. Natl. Acad. Sci. USA 86: 9268-9272; Martin et al. (1991)Methods Enzymol. 203: 121-153; Pedersen et al. (1992) Immunomethods 1:126; and Rees et al. (1996) In Sternberg M. J. E. (ed.), ProteinStructure Prediction, Oxford University Press, Oxford, pp. 141-172.

Specificity determining regions (SDRs) are residues within CDRs thatdirectly interact with antigen. The SDRs correspond to hypervariableresidues. See (Padlan et al. (1995) FASEB J. 9: 133-139).

Framework residues are those residues of antibody variable regions otherthan hypervariable or CDR residues. Framework residues may be derivedfrom a naturally occurring human antibody, such as a human frameworkthat is substantially similar to a framework region of the A1, A2, or A3antibodies. Artificial framework sequences that represent a consensusamong individual sequences may also be used. When selecting a frameworkregion for humanization, sequences that are widely represented in humansmay be preferred over less populous sequences. Additional mutations ofthe human framework acceptor sequences may be made to restore murineresidues believed to be involved in antigen contacts and/or residuesinvolved in the structural integrity of the antigen-binding site, or toimprove antibody expression. A peptide structure prediction may be usedto analyze the humanized variable heavy and light region sequences toidentify and avoid post-translational protein modification sitesintroduced by the humanization design.

Humanized antibodies may be prepared using any one of a variety ofmethods including veneering, grafting of complementarity determiningregions (CDRs), grafting of abbreviated CDRs, grafting of specificitydetermining regions (SDRs), and Frankenstein assembly, as describedbelow. Humanized antibodies also include superhumanized antibodies, inwhich one or more changes have been introduced in the CDRs. For example,human residues may be substituted for non-human residues in the CDRs.These general approaches may be combined with standard mutagenesis andsynthesis techniques to produce an anti-5T4 antibody of any desiredsequence.

Veneering is based on the concept of reducing potentially immunogenicamino acid sequences in a rodent or other non-human antibody byresurfacing the solvent accessible exterior of the antibody with humanamino acid sequences. Thus, veneered antibodies appear less foreign tohuman cells than the unmodified non-human antibody. See Padlan (1991)Mol. Immunol. 28:489-98. A non-human antibody is veneered by identifyingexposed exterior framework region residues in the non-human antibody,which are different from those at the same positions in frameworkregions of a human antibody, and replacement of the identified residueswith amino acids that typically occupy these same positions in humanantibodies.

Grafting of CDRs is performed by replacing one or more CDRs of anacceptor antibody (e.g., a human antibody or other antibody comprisingdesired framework residues) with CDRs of a donor antibody (e.g., anon-human antibody). Acceptor antibodies may be selected based onsimilarity of framework residues between a candidate acceptor antibodyand a donor antibody. For example, according to the Frankensteinapproach, human framework regions are identified as having substantialsequence homology to each framework region of the relevant non-humanantibody, and CDRs of the non-human antibody are grafted onto thecomposite of the different human framework regions. A related methodalso useful for preparation of antibodies of the invention is describedin U.S. Patent Application Publication No. 2003/0040606.

Grafting of abbreviated CDRs is a related approach. Abbreviated CDRsinclude the specificity-determining residues and adjacent amino acids,including those at positions 27d-34, 50-55 and 89-96 in the light chain,and at positions 31-35b, 50-58, and 95-101 in the heavy chain (numberingconvention of (Kabat et al. (1987)). See (Padlan et al. (1995) FASEB J.9: 133-9). Grafting of specificity-determining residues (SDRs) ispremised on the understanding that the binding specificity and affinityof an antibody combining site is determined by the most highly variableresidues within each of the complementarity determining regions (CDRs).Analysis of the three-dimensional structures of antibody-antigencomplexes, combined with analysis of the available amino acid sequencedata may be used to model sequence variability based on structuraldissimilarity of amino acid residues that occur at each position withinthe CDR. SDRs are identified as minimally immunogenic polypeptidesequences consisting of contact residues. See Padlan et al. (1995) FASEBJ. 9: 133-139.

In general, human acceptor frameworks are selected on the basis thatthey are substantially similar to the framework regions of the donorantibodies, or which are most similar to the consensus sequence of thevariable region subfamily. Following grafting, additional changes may bemade in the donor and/or acceptor sequences to optimize antibodybinding, functionality, codon usage, expression levels, etc, includingintroduction of non-human residues into the framework regions. See e.g.,PCT International Publication No. WO 91/09967.

For grafting of CDRs onto a heavy chain variable framework region,useful framework sequences may be derived from a DP-21 (VH7), DP-54(VH3-07), DP-47 (VH3-23), DP-53 (VH-74), DP-49 (VH3-30), DP-48 (VH3-13),DP-75, DP-8(VH1-2), DP-25, VI-2b and VI-3 (VH1-03), DP-15 and V1-8(VH1-08), DP-14 and V1-18 (VH1-18), DP-5 and V1-24P (VH1-24), DP-4(VH1-45), DP-7 (VH1-46), DP-10, DA-6 and YAC-7 (VH1-69), DP-88 (VH1-e),DP-3 and DA-8 (VH1-f). Representative heavy chain variable regionscontaining framework residues for humanization are set forth as SEQ IDNOs:13-24 and 88-93. Representative frameworks that represent aconsensus of VH1 framework residues are set forth as SEQ ID NOs:25-27.See also FIGS. 10A-10B.

For grafting of CDRs onto a light chain variable framework region,useful framework sequences may be derived from a DPK24 subgroup IV germline clone, a VκIII subgroup (DPK23, DPK22, DPK20, DPK21), or a VκIsubgroup germ line clone (DPK9, DPK1, O2, DPK7). Representative lightchain variable regions containing framework residues for humanizationare set forth as SEQ ID NOs:28-34, 35-44, and 94-99. See FIGS. 11-14.

Representative humanized anti-5T4 antibodies of the invention includeantibodies having one or more CDRs of a non-human anti-5T4 antibodyselected from CDRs of a heavy chain variable region of any one of SEQ IDNOs:2, 6, or 10, or a light chain variable region of any one of SEQ IDNOs:4, 8, or 12. For example, humanized anti-5T4 antibodies may comprisetwo or more CDRs selected from CDRs of a heavy chain variable region ofany one of SEQ ID NOs:2, 6, or 10, or a light chain variable region ofany one of SEQ ID NOs:4, 8, or 12. Humanized anti-5T4 antibodies mayalso comprise a heavy chain comprising a variable region having two orthree CDRs of any one of SEQ ID NOs:2, 6, or 10, and a light chaincomprising a variable region having two or three CDRs of any one of SEQID NOs:4, 8, or 12.

Humanized anti-5T4 antibodies of the invention may be constructedwherein the variable region of a first chain (i.e., the light chainvariable region or the heavy chain variable region) is humanized, andwherein the variable region of the second chain is not humanized (i.e.,a variable region of an antibody produced in a non-human species). Theseantibodies are a type of humanized antibody referred to assemi-humanized antibodies. Non-human anti-5T4 antibodies that may beused to prepare semi-humanized antibodies include the A1, A2, and A3antibodies, as disclosed herein, as well as the H8 antibody described inPCT International Publication No. WO 98/55607 and in Forsberg et al.(1997) J. Biol. Chem. 272(19):124430-12436, or the rat monoclonalantibody described in Woods et al. (2002) Biochem. J. 366: 353-65). Forexample, a semi-humanized anti-5T4 antibody can comprise a heavy chainvariable region set for as amino acids 1-119 of SEQ ID NO:49 or aminoacids of a humanized A1, A2, or A3 heavy chain variable region depictedin FIGS. 9A-9C, and a light chain variable region of any one of SEQ IDNOs:4, 8, or 12.

The constant regions of chimeric and humanized anti-5T4 antibodies maybe derived from constant regions of any one of IgA, IgD, IgE, IgG, IgM,any isotypes thereof (e.g., IgG1, IgG2, IgG3, or IgG4 isotypes of IgG),as well as mutated versions thereof. The choice of a human isotype andmodification of particular amino acids in the isotype may enhance oreliminate activation of host defense mechanisms and alter antibodybiodistribution. See (Reff et al. (2002) Cancer Control 9: 152-66).Representative constant regions useful for preparing chimeric andhumanized antibodies of the invention are set forth as SEQ ID NOs:45-47. Human lambda light chain constant regions, included variant ormutant versions, may also be used. For cloning of sequences encodingimmunoglobulin constant regions, intronic sequences may be deleted.

Chimeric and humanized anti-5T4 antibodies may be constructed usingstandard techniques known in the art. For example, variable regions maybe prepared by annealing together overlapping oligonucleotides encodingthe variable regions and ligating them into an expression vectorcontaining a human antibody constant region. See e.g., Harlow & Lane(1988) Antibodies: A Laboratory Manual, Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, N.Y. and U.S. Pat. Nos. 4,196,265; 4,946,778;5,091,513; 5,132,405; 5,260,203; 5,677,427; 5,892,019; 5,985,279;6,054,561. Tetravalent antibodies (H₄L₄) comprising two intacttetrameric antibodies, including homodimers and heterodimers, may beprepared, for example, as described in PCT International Publication No.WO 02/096948. Antibody dimers may also be prepared via introduction ofcysteine residue(s) in the antibody constant region, which promoteinterchain disulfide bond formation, by use of heterobifunctionalcross-linkers (Wolff et al. (1993) Cancer Res. 53: 2560-5), or byrecombinant production to include a dual constant region (Stevenson etal. (1989) Anticancer Drug Des. 3: 219-30). Antigen-binding fragments ofantibodies of the invention may be prepared, for example, by expressionof truncated antibody sequences, or by post-translation digestion offull-length antibodies.

Variants of anti-5T4 antibodies of the invention, i.e., the A1, A2, andA3 antibodies as well as chimeric and humanized versions thereof, may bereadily prepared to include various changes, substitutions, insertions,and deletions. For example, antibody sequences may be optimized forcodon usage in the cell type used for antibody expression. To increasethe serum half life of the antibody, a salvage receptor binding epitopemay be incorporated, if not present already, into the antibody heavychain sequence. See U.S. Pat. No. 5,739,277. Additional modifications toenhance antibody stability include modification of IgG4 to replace theserine at residue 241 with proline. See Angal et al. (1993) Mol.Immunol. 30: 105-108. Other useful changes include substitutions asrequired to optimize efficiency in conjugating the antibody with a drug.For example, an antibody may be modified at its carboxyl terminus toinclude amino acids for drug attachment, for example one or morecysteine residues may be added. The constant regions may be modified tointroduce sites for binding of carbohydrates or other moieties.

Variants of anti-5T4 antibodies of the invention may be produced usingstandard recombinant techniques, including site-directed mutagenesis, orrecombination cloning. A diversified repertoire of anti-5T4 antibodiesmay be prepared via gene arrangement and gene conversion methods intransgenic non-human animals (U.S. Patent Publication No. 2003/0017534),which are then tested for relevant activities using functional assays.In particular embodiments of the invention, anti-5T4 variants areobtained using an affinity maturation protocol for mutating CDRs (Yanget al. (1995) J. Mol. Biol. 254: 392-403), chain shuffling (Marks et al.(1992) Biotechnology (NY) 10: 779-783), use of mutator strains of E.coli (Low et al. (1996) J. Mol. Biol. 260: 359-368), DNA shuffling(Patten et al. (1997) Curr. Opin. Biotechnol. 8: 724-733), phage display(Thompson et al. (1996) J. Mol. Biol. 256: 77-88), and sexual PCR(Crameri et al. (1998) Nature 391: 288-291). For immunotherapyapplications, relevant functional assays include specific binding tohuman 5T4 antigen, antibody internalization, and targeting to a tumorsite(s) when administered to a tumor-bearing animal, as described hereinbelow.

The present invention further provides cells and cell lines expressinganti-5T4 antibodies of the invention. Representative host cells includemammalian and human cells, such as CHO cells, HEK-293 cells, HeLa cells,CV-1 cells, and COS cells. Methods for generating a stable cell linefollowing transformation of a heterologous construct into a host cellare known in the art. Representative non-mammalian host cells includeinsect cells (Potter et al. (1993) Int. Rev. Immunol. 10(2-3):103-112).Antibodies may also be produced in transgenic animals (Houdebine (2002)Curr. Opin. Biotechnol. 13(6):625-629) and transgenic plants (Schillberget al. (2003) Cell Mol. Life. Sci. 60(3):433-45).

II. Anti-5T4 Nucleic Acids and Polypeptides

The present invention further provides isolated nucleic acids encodinganti-5T4 heavy chain and light chain variable regions, and isolatedpolypeptides encoded by the disclosed nucleic acids. Nucleic acids andpolypeptides of the invention include the nucleotide and amino acidsequences of the A1, A2, and A3 variable regions, humanized A1, A2, andA3 variable regions, and variants thereof. The isolated nucleic acidsand polypeptides may be used to prepare chimeric and humanized anti-5T4antibodies.

II.A. Anti-5T4 Nucleic Acids

Nucleic acids are deoxyribonucleotides or ribonucleotides and polymersthereof in single-stranded, double-stranded, or triplexed form. Unlessspecifically limited, nucleic acids may contain known analogues ofnatural nucleotides that have similar properties as the referencenatural nucleic acid. Nucleic acids include genes, cDNAs, mRNAs, andcRNAs. Nucleic acids may be synthesized, or may be derived from anybiological source, including any organism. Representative methods forcloning nucleic acids that encode anti-5T4 antibodies are described inExamples 1 and 7.

Representative nucleic acids of the invention comprise the nucleotidesequence of any one of SEQ ID NOs:1, 3, 5, 7, 9, 11, and 48. Inparticular, nucleic acids encoding the A1, A2, and A3 heavy chainvariable regions comprise nucleotides 58-41 of SEQ ID NO:1, nucleotides55-405 of SEQ ID NO:5, and nucleotides 58-423 of SEQ ID NO:9,respectively, which encode heavy chain variable regions having the aminoacid sequences set forth as residues 20-138 of SEQ ID NO:2, residues19-135 of SEQ ID NO:6, and residues 20-141 of SEQ ID NO:10,respectively. A nucleic acid encoding a humanized A1 heavy chainvariable region comprises nucleotides 1-358 of SEQ ID NO:48. Nucleicacids encoding the A1, A2, and A3 light chain variable regions comprisenucleotides 61-381 of SEQ ID NO:3, nucleotides 67-390 of SEQ ID NO:7,and nucleotides 61-381 of SEQ ID NO:11, respectively, which encode heavychain variable regions having the amino acid sequences set forth asresidues 21-127 of SEQ ID NO:4, residues 23-130 of SEQ ID NO:8, andresidues 21-127 of SEQ ID NO:12, respectively. Additional nucleic acidsof the invention comprise nucleotides encoding the humanized A1, A2, andA3 variable regions depicted in FIGS. 9A-9C.

Nucleic acids of the invention may also comprise a nucleotide sequencethat is substantially identical to any one of SEQ ID NOs:1, 3, 5, 7, 9,11, and 48, including nucleotide sequences that are at least 90%identical to the variable region encoding sequences of any one of SEQ IDNOs:1, 3, 5, 7, 9, and 11, such as at least about 91% identical or least92% identical, such as at least 93% identical, or at least 94%identical, or at least 95% identical, or at least 96% identical, or atleast 97% identical, or at least 98% identical, or at least 99%identical. For example, nucleic acids of the invention may comprise (a)a nucleotide sequence that is least 98% identical to the variable regionencoding sequence of SEQ ID NO:1; (b) a nucleotide sequence that is atleast 97% identical to the variable region encoding sequence of SEQ IDNO:3; (c) a nucleotide sequence that is at least 98% identical to thevariable region encoding sequence of SEQ ID NO:5; (d) a nucleotidesequence that is at least 98% identical to the variable region encodingsequence of SEQ ID NO:7; (e) a nucleotide sequence that is at least 99%identical to the variable region encoding sequence of SEQ ID NO:11; or(f) a nucleotide sequence that is at least 89% identical to the variableregion encoding sequence of SEQ ID NO:48. Sequences are compared formaximum correspondence using a sequence comparison algorithm using thefull-length variable region encoding sequence of any one of SEQ IDNOs:1, 3, 5, 7, 9, 11, 48, or nucleotide sequences encoding humanizedA1, A2, and A3 variable region sequences depicted in FIGS. 9A-9H as thequery sequence, as described herein below, or by visual inspection. Seealso Example 1 and Table 1, and Example 7 and Table 11.

Substantially identical sequences may be polymorphic sequences, i.e.,alternative sequences or alleles in a population. An allelic differencemay be as small as one base pair. Substantially identical sequences mayalso comprise mutagenized sequences, including sequences comprisingsilent mutations. A mutation may comprise one or more residue changes, adeletion of one or more residues, or an insertion of one or moreadditional residues.

Substantially identical nucleic acids are further identified as nucleicacids that hybridize specifically to or hybridize substantially to thefull length of any one of SEQ ID NOs:1, 3, 5, 7, 9, 11, or 48; the fulllength of a variable region encoding sequence of any one of SEQ IDNOs:1, 3, 5, 7, 9, 11, or 48; or nucleotide sequences encoding humanizedA1, A2, and A3 variable region sequences depicted in FIGS. 9A-9H, understringent conditions. In the context of nucleic acid hybridization, twonucleic acid sequences being compared may be designated a probe and atarget. A probe is a reference nucleic acid molecule, and a target is atest nucleic acid molecule, often found within a heterogeneouspopulation of nucleic acid molecules. A target sequence is synonymouswith a test sequence.

For hybridization studies, useful probes are complementary to or mimicat least an about 14 to 40 nucleotide sequence of a nucleic acidmolecule of the present invention. Preferably, probes comprise 14 to 20nucleotides, or even longer where desired, such as 30, 40, 50, 60, 100,200, 300, or 500 nucleotides or up to the full length of any one of SEQID NOs:1, 3, 5, 7, 9, 11, or 48; the full length of a variable regionencoding sequence of any one of SEQ ID NOs:1, 3, 5, 7, 9, 11, or 48; ornucleotide sequences encoding humanized A1, A2, and A3 variable regionsequences depicted in FIGS. 9A-9C. Such fragments may be readilyprepared, for example, by chemical synthesis of the fragment, byapplication of nucleic acid amplification technology, or by introducingselected sequences into recombinant vectors for recombinant production.

Specific hybridization refers to the binding, duplexing, or hybridizingof a molecule only to a particular nucleotide sequence under stringentconditions when that sequence is present in a complex nucleic acidmixture (e.g., total cellular DNA or RNA). Specific hybridization mayaccommodate mismatches between the probe and the target sequencedepending on the stringency of the hybridization conditions.

Stringent hybridization conditions and stringent hybridization washconditions in the context of nucleic acid hybridization experiments suchas Southern and Northern blot analysis are both sequence- andenvironment-dependent. Longer sequences hybridize specifically at highertemperatures. An extensive guide to the hybridization of nucleic acidsis found in Tijssen (1993) Laboratory Techniques in Biochemistry andMolecular Biology-Hybridization with Nucleic Acid Probes, part I chapter2, Elsevier, New York, N.Y. Generally, highly stringent hybridizationand wash conditions are selected to be about 5° C. lower than thethermal melting point (T_(m)) for the specific sequence at a definedionic strength and pH. Typically, under stringent conditions a probewill hybridize specifically to its target subsequence, but to no othersequences.

The T_(m) is the temperature (under defined ionic strength and pH) atwhich 50% of the target sequence hybridizes to a perfectly matchedprobe. Very stringent conditions are selected to be equal to the T_(m)for a particular probe. An example of stringent hybridization conditionsfor Southern or Northern Blot analysis of complementary nucleic acidshaving more than about 100 complementary residues is overnighthybridization in 50% formamide with 1 mg of heparin at 42° C. An exampleof highly stringent wash conditions is 15 minutes in 0.1×SSC at 65° C.An example of stringent wash conditions is 15 minutes in 0.2×SSC bufferat 65° C. See Sambrook et al., eds (1989) Molecular Cloning: ALaboratory Manual, Cold Spring Harbor Laboratory Press, Cold SpringHarbor, N.Y., for a description of SSC buffer. Often, a high stringencywash is preceded by a low stringency wash to remove background probesignal. An example of medium stringency wash conditions for a duplex ofmore than about 100 nucleotides, is 15 minutes in 1×SSC at 45° C. Anexample of low stringency wash for a duplex of more than about 100nucleotides, is 15 minutes in 4× to 6×SSC at 40° C. For short probes(e.g., about 10 to 50 nucleotides), stringent conditions typicallyinvolve salt concentrations of less than about 1M Na⁺ ion, typicallyabout 0.01 to 1M Na⁺ ion concentration (or other salts) at pH 7.0-8.3,and the temperature is typically at least about 30° C. Stringentconditions may also be achieved with the addition of destabilizingagents such as formamide. In general, a signal to noise ratio of 2-fold(or higher) than that observed for an unrelated probe in the particularhybridization assay indicates detection of a specific hybridization.

The following are examples of hybridization and wash conditions that maybe used to identify nucleotide sequences that are substantiallyidentical to reference nucleotide sequences of the present invention: aprobe nucleotide sequence preferably hybridizes to a target nucleotidesequence in 7% sodium dodecyl sulphate (SDS), 0.5M NaPO₄, 1 mM EDTA at50° C. followed by washing in 2×SSC, 0.1% SDS at 50° C.; morepreferably, a probe and target sequence hybridize in 7% sodium dodecylsulphate (SDS), 0.5M NaPO₄, 1 mM EDTA at 50° C. followed by washing in1×SSC, 0.1% SDS at 50° C.; more preferably, a probe and target sequencehybridize in 7% sodium dodecyl sulphate (SDS), 0.5M NaPO₄, 1 mM EDTA at50° C. followed by washing in 0.5×SSC, 0.1% SDS at 50° C.; morepreferably, a probe and target sequence hybridize in 7% sodium dodecylsulphate (SDS), 0.5M NaPO₄, 1 mM EDTA at 50° C. followed by washing in0.1×SSC, 0.1% SDS at 50° C.; more preferably, a probe and targetsequence hybridize in 7% sodium dodecyl sulphate (SDS), 0.5M NaPO₄, 1 mMEDTA at 50° C. followed by washing in 0.1×SSC, 0.1% SDS at 65° C.

A further indication that two nucleic acid sequences are substantiallyidentical is that proteins encoded by the nucleic acids aresubstantially identical, share an overall three-dimensional structure,or are biologically functional equivalents. These terms are definedfurther herein below. Nucleic acid molecules that do not hybridize toeach other under stringent conditions are still substantially identicalif the corresponding proteins are substantially identical. This mayoccur, for example, when two nucleotide sequences compriseconservatively substituted variants as permitted by the genetic code.

Conservatively substituted variants are nucleic acid sequences havingdegenerate codon substitutions wherein the third position of one or moreselected (or all) codons is substituted with mixed-base and/ordeoxyinosine residues. See Batzer et al. (1991) Nucleic Acids Res.19:5081; Ohtsuka et al. (1985) J. Biol. Chem. 260:2605-2608; andRossolini et al. (1994) Mol. Cell Probes 8:91-98.

Nucleic acids of the invention also comprise nucleic acids complementaryto any one of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 48, or nucleotide sequencesencoding humanized A1, A2, and A3 variable region sequences depicted inFIGS. 9A-9C, and subsequences and elongated sequences of SEQ ID NOs: 1,3, 5, 7, 9, 11, 48, or nucleotide sequences encoding humanized A1, A2,and A3 variable region sequences depicted in FIGS. 9A-9C, andcomplementary sequences thereof. Complementary sequences are twonucleotide sequences that comprise antiparallel nucleotide sequencescapable of pairing with one another upon formation of hydrogen bondsbetween base pairs. As used herein, the term complementary sequencesmeans nucleotide sequences which are substantially complementary, as maybe assessed by the same nucleotide comparison methods set forth below,or is defined as being capable of hybridizing to the nucleic acidsegment in question under relatively stringent conditions such as thosedescribed herein. A particular example of a complementary nucleic acidsegment is an antisense oligonucleotide.

A subsequence is a sequence of nucleic acids that comprises a part of alonger nucleic acid sequence. An exemplary subsequence is a probe,described herein above, or a primer. The term primer as used hereinrefers to a contiguous sequence comprising about 8 or moredeoxyribonucleotides or ribonucleotides, preferably 10-20 nucleotides,and more preferably 20-30 nucleotides of a selected nucleic acidmolecule. The primers of the invention encompass oligonucleotides ofsufficient length and appropriate sequence so as to provide initiationof polymerization on a nucleic acid molecule of the present invention.

An elongated sequence comprises additional nucleotides (or otheranalogous molecules) incorporated into the nucleic acid. For example, apolymerase (e.g., a DNA polymerase) may add sequences at the 3′ terminusof the nucleic acid molecule. In addition, the nucleotide sequence maybe combined with other DNA sequences, such as promoters, promoterregions, enhancers, polyadenylation signals, intronic sequences,additional restriction enzyme sites, multiple cloning sites, and othercoding segments. Thus, the invention also provides vectors comprisingthe disclosed nucleic acids, including vectors for recombinantexpression, wherein a nucleic acid of the invention is operativelylinked to a functional promoter. When operatively linked to a nucleicacid, a promoter is in functional combination with the nucleic acid suchthat the transcription of the nucleic acid is controlled and regulatedby the promoter region. Vectors refer to nucleic acids capable ofreplication in a host cell, such as plasmids, cosmids, and viralvectors.

Nucleic acids of the present invention may be cloned, synthesized,altered, mutagenized, or combinations thereof. Standard recombinant DNAand molecular cloning techniques used to isolate nucleic acids are knownin the art. Site-specific mutagenesis to create base pair changes,deletions, or small insertions is also known in the art. See e.g.,Sambrook et al. (eds.) (1989) Molecular Cloning: A Laboratory Manual.Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.; Silhavyet al. (1984) Experiments with Gene Fusions. Cold Spring HarborLaboratory Press, Cold Spring Harbor, N.Y.; Glover & Hames (1995) DNACloning: A Practical Approach, 2nd ed. IRL Press at Oxford UniversityPress, Oxford/New York; Ausubel (ed.) (1995) Short Protocols inMolecular Biology, 3rd ed. Wiley, New York.

II.B. Anti-5T4 Polypeptides

The present invention also provides isolated anti-5T4 polypeptides.Polypeptides and proteins each refer to a compound made up of a singlechain of amino acids joined by peptide bonds. Representative heavy chainvariable region polypeptides are set forth as residues 20-138 of SEQ IDNO:2, residues 19-135 of SEQ ID NO:6, residues 20-141 of SEQ ID NO:10,and residues 1-119 of SEQ ID NO:49. Representative light chain variableregion polypeptides are set forth as residues 21-127 of SEQ ID NO:4,residues 23-130 of SEQ ID NO:8, and residues 21-127 of SEQ ID NO:12.Additional polypeptides of the invention comprise amino acids of thehumanized A1, A2, and A3 variable regions depicted in FIGS. 9A-9C.

Additional polypeptides of the invention include heavy chain and lightchain variable region polypeptides that are substantially similar to thedisclosed anti-5T4 polypeptides, such as at least about 90% identical tothe variable regions of SEQ ID NOs:2, 4, 6, 8, 10, 12, and 49, forexample, at least about 91% identical, least 92% identical, at least 93%identical, at least 94% identical, at least 95% identical, at least 96%identical, at least 97% identical, at least 98% identical, or at least99% identical. Sequences are compared for maximum correspondence using asequence comparison algorithm using the full-length sequence of any oneof SEQ ID NOs:2, 4, 6, 8, 10, 12, 49, or any one of the humanized A1,A2, or A3 variable regions depicted in FIGS. 9A-9C as the querysequence, or the variable region sequence thereof, or by visualinspection. The invention further encompasses polypeptides encoded byany one of the nucleic acids disclosed herein.

For example, representative polypeptides of the invention include (a)polypeptides having an amino acid sequence that is at least 85% similarto residues 20-138 of SEQ ID NO:2; (b) polypeptides having an amino acidsequence that is at least 94% similar to residues 21-127 of SEQ ID NO:4;(c) polypeptides having an amino acid sequence that is at least 86%similar to residues 19-135 of SEQ ID NO:6; (d) polypeptides having anamino acid sequence that is at least 96% similar to residues 23-130 ofSEQ ID NO:8; (e) polypeptides having an amino acid sequence that is atleast 91% similar to residues 20-141 of SEQ ID NO:10; (f) polypeptideshaving an amino acid sequence that is at least 98% similar to residues21-127 of SEQ ID NO:12; and (g) polypeptides having an amino acidsequence that is at least 90% similar to residues 1-119 of SEQ ID NO:49.See Example 1 and Table 2, and Example 7 and Table 11.

Polypeptides of the invention may comprise naturally occurring aminoacids, synthetic amino acids, genetically encoded amino acids,non-genetically encoded amino acids, and combinations thereof.Polypeptides may include both L-form and D-form amino acids.

Representative non-genetically encoded amino acids include but are notlimited to 2-aminoadipic acid; 3-aminoadipic acid; 1-aminopropionicacid; 2-aminobutyric acid; 4-aminobutyric acid (piperidinic acid);6-aminocaproic acid; 2-aminoheptanoic acid; 2-aminoisobutyric acid;3-aminoisobutyric acid; 2-aminopimelic acid; 2,4-diaminobutyric acid;desmosine; 2,2′-diaminopimelic acid; 2,3-diaminopropionic acid;N-ethylglycine; N-ethylasparagine; hydroxylysine; allo-hydroxylysine;3-hydroxyproline; 4-hydroxyproline; isodesmosine; allo-isoleucine;N-methylglycine (sarcosine); N-methylisoleucine; N-methylvaline;norvaline; norleucine; and ornithine.

Representative derivatized amino acids include, for example, thosemolecules in which free amino groups have been derivatized to form aminehydrochlorides, p-toluene sulfonyl groups, carbobenzoxy groups,t-butyloxycarbonyl groups, chloroacetyl groups or formyl groups. Freecarboxyl groups may be derivatized to form salts, methyl and ethylesters or other types of esters or hydrazides. Free hydroxyl groups maybe derivatized to form O-acyl or O-alkyl derivatives. The imidazolenitrogen of histidine may be derivatized to form N-im-benzylhistidine.

The present invention also provides fragments of an anti-5T4 polypeptideof the invention, for example, fragments constituting a 5T4 antigenbinding site. Polypeptide sequences that are longer than the disclosedsequences are also provided. For example, one or more amino acids may beadded to the N-terminus or C-terminus of an antibody polypeptide. Suchadditional amino acids may be employed in a variety of applications,including but not limited to purification applications. Methods ofpreparing elongated proteins are known in the art.

Anti-5T4 polypeptides of the invention include proteins comprising aminoacids that are conservatively substituted variants of any one of SEQ IDNOs:2, 4, 6, 8, 10, 12, or 49. A conservatively substituted variantrefers to a polypeptide comprising an amino acid in which one or moreresidues have been conservatively substituted with a functionallysimilar residue.

Examples of conservative substitutions include the substitution of onenon-polar (hydrophobic) residue such as isoleucine, valine, leucine ormethionine for another; the substitution of one polar (hydrophilic)residue for another such as between arginine and lysine, betweenglutamine and asparagine, between glycine and serine; the substitutionof one basic residue such as lysine, arginine or histidine for another;or the substitution of one acidic residue, such as aspartic acid orglutamic acid for another.

Isolated polypeptides of the invention may be purified and characterizedusing a variety of standard techniques that are known to the skilledartisan. See e.g., Schröder & Lübke (1965) The Peptides. Academic Press,New York; Bodanszky (1993) Principles of Peptide Synthesis, 2nd rev. ed.Springer-Verlag, Berlin/New York; Ausubel (ed.) (1995) Short Protocolsin Molecular Biology, 3rd ed. Wiley, New York.

II.C. Nucleotide and Amino Acid Sequence Comparisons

The terms identical or percent identity in the context of two or morenucleotide or protein sequences, refer to two or more sequences orsubsequences that are the same or have a specified percentage of aminoacid residues or nucleotides that are the same, when compared andaligned for maximum correspondence, as measured using one of thesequence comparison algorithms disclosed herein or by visual inspection.

The term substantially identical in regards to a nucleotide or proteinsequence means that a particular sequence varies from the sequence of anaturally occurring sequence by one or more deletions, substitutions, oradditions, the net effect of which is to retain biological function ofan anti-5T4 nucleic acid or polypeptide.

For comparison of two or more sequences, typically one sequence acts asa reference sequence to which one or more test sequences are compared.When using a sequence comparison algorithm, test and reference sequencesare entered into a computer program, subsequence coordinates aredesignated if necessary, and sequence algorithm program parameters areselected. The sequence comparison algorithm then calculates the percentsequence identity for the designated test sequence(s) relative to thereference sequence, based on the selected program parameters.

Optimal alignment of sequences for comparison may be conducted, forexample, by the local homology algorithm of Smith & Waterman (1981) Adv.Appl. Math 2:482-489, by the homology alignment algorithm of Needleman &Wunsch (1970) J. Mol. Biol. 48:443-453, by the search for similaritymethod of Pearson & Lipman (1988) Proc. Natl. Acad. Sci. USA85:2444-2448, by computerized implementations of these algorithms (GAP,BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package,Genetics Computer Group, Madison, Wis.), or by visual inspection. Seegenerally, Ausubel (ed.) (1995) Short Protocols in Molecular Biology,3rd ed. Wiley, New York.

A preferred algorithm for determining percent sequence identity andsequence similarity is the BLAST algorithm, which is described inAltschul et al. (1990) J. Mol. Biol. 215:403-410. Software forperforming BLAST analyses is publicly available through the NationalCenter for Biotechnology Information (web site www.ncbi.nlm.nih.gov).The BLAST algorithm parameters determine the sensitivity and speed ofthe alignment. For comparison of two nucleotide sequences, the BLASTndefault parameters are set at W=11 (wordlength) and E=10 (expectation),and also include use of a low-complexity filter to mask residues of thequery sequence having low compositional complexity. For comparison oftwo amino acid sequences, the BLASTp program default parameters are setat W=3 (wordlength), E=10 (expectation), use of the BLOSUM62 scoringmatrix, gap costs of existence=11 and extension=1, and use of alow-complexity filter to mask residues of the query sequence having lowcompositional complexity. See Example 1.

III. Anti-5T4 Antibody/Drug Conjugates

The present invention further provides antibody/drug conjugatescomprising an anti-5T4 antibody of the invention. Also provided aremethods for preparing the antibody/drug conjugates, such that the drugis bound to the antibody either directly or indirectly. Antibody/drugconjugates of the invention have the general formula 5T4Ab(-X—W)_(m)

wherein:

5T4Ab is an anti-5T4 antibody or antibody fragment as described herein;

X is a linker that comprises a product of any reactive group that mayreact with an anti-5T4 antibody or antibody fragment;

W is a drug;

m is the average loading for a purified conjugation product (e.g., msuch that the drug constitutes about 3-10% of the conjugate by weight);and

(—X—W)_(m) is a drug derivative.

Also provided are methods for preparing antibody/drug conjugates of theinvention. As one example, an antibody/drug conjugate of the formula5T4Ab(-X—W)_(m) may be prepared by (a) adding the drug derivative to theanti-5T4 antibody wherein the drug is 3-10% by weight of the anti-5T4antibody; (b) incubating the drug derivative and the anti-5T4 antibodyin a non-nucleophilic, protein-compatible, buffered solution having a pHin a range from about 7 to 9 to produce an antibody/drug conjugate,wherein the solution further compromises (i) a suitable organiccosolvent, and (ii) and one or more additives comprising at least onebile acid or its salt, and wherein the incubation is conducted at atemperature ranging from about 30° C. to about 35° C. for a period oftime ranging from about 15 minutes to about 24 hours; and (c) subjectingthe conjugate produced in step (b) to a chromatographic separationprocess to separate antibody/drug conjugates with a loading in the rangeof 3-10% by weight drug and with low conjugated fraction (LCF) fromunconjugated anti-5T4 antibody, drug derivative, and aggregatedconjugates.

III.A. Drugs

A drug is any substance having biological or detectable activity, forexample, therapeutic agents, detectable labels, binding agents, etc.,and prodrugs, which are metabolized to an active agent in vivo. A drugmay also be a drug derivative, wherein a drug has been functionalized toenable conjugation with an antibody of the invention. Generally, thesetypes of conjugates are referred to as immunoconjugates.

Therapeutic agents are compositions that may be used to treat or preventa condition in a subject in need thereof. Therapeutic agents useful inthe invention include anti-cancer agents, i.e., agents havinganti-cancer activity in 5T4-expressing cells such as cancer cells fromsquamous/adenomatous lung carcinoma (non-small-cell lung carcinoma),invasive breast carcinoma, colorectal carcinoma, gastric carcinoma,squamous cervical carcinoma, invasive endometrial adenocarcinoma,invasive pancreas carcinoma, ovarian carcinoma, squamous vesicalcarcinoma, and choriocarcinoma.

Representative therapeutic drugs include cytotoxins, radioisotopes,chemotherapeutic agents, immunomodulatory agents, anti-angiogenicagents, anti-proliferative agents, pro-apoptotic agents, and cytostaticand cytolytic enzymes (e.g., RNAses). A drug may also include atherapeutic nucleic acid, such as a gene encoding an immunomodulatoryagent, an anti-angiogenic agent, an anti-proliferative agent, or apro-apoptotic agent. These drug descriptors are not mutually exclusive,and thus a therapeutic agent may be described using one or more of theabove-noted terms. For example, selected radioisotopes are alsocytotoxins. Therapeutic agents may be prepared as pharmaceuticallyacceptable salts, acids or derivatives of any of the above. Generally,conjugates having a radioisotope as the drug are referred to asradioimmunoconjugates and those having a chemotherapeutic agent as thedrug are referred to as chemoimmunoconjugates.

Examples of suitable drugs for use in immunoconjugates include thetaxanes, maytansines, CC-1065 and the duocarmycins, the calicheamicinsand other enediynes, and the auristatins. Other examples include theanti-folates, vinca alkaloids, and the anthracyclines. Plant toxins,other bioactive proteins, enzymes (i.e., ADEPT), radioisotopes,photosensitizers (i.e., for photodynamic therapy) can also be used inimmunoconjugates. In addition, conjugates can be made using secondarycarriers as the cytotoxic agent, such as liposomes or polymers, forexample.

The term cytotoxin generally refers to an agent that inhibits orprevents the function of cells and/or results in destruction of cells.Representative cytotoxins include antibiotics, inhibitors of tubulinpolymerization, alkylating agents that bind to and disrupt DNA, andagents that disrupt protein synthesis or the function of essentialcellular proteins such as protein kinases, phosphatases, topoisomerases,enzymes, and cyclins. Representative cytotoxins include, but are notlimited to, doxorubicin, daunorubicin, idarubicin, aclarubicin,zorubicin, mitoxantrone, epirubicin, carubicin, nogalamycin, menogaril,pitarubicin, valrubicin, cytarabine, gemcitabine, trifluridine,ancitabine, enocitabine, azacitidine, doxifluridine, pentostatin,broxuridine, capecitabine, cladribine, decitabine, floxuridine,fludarabine, gougerotin, puromycin, tegafur, tiazofurin, adriamycin,cisplatin, carboplatin, cyclophosphamide, dacarbazine, vinblastine,vincristine, mitoxantrone, bleomycin, mechlorethamine, prednisone,procarbazine, methotrexate, fluorouracils, etoposide, taxol, taxolanalogs, platins such as cis-platin and carbo-platin, mitomycin,thiotepa, taxanes, vincristine, daunorubicin, epirubicin, actinomycin,authramycin, azaserines, bleomycins, tamoxifen, idarubicin,dolastatins/auristatins, hemiasterlins, esperamicins and maytansinoids.

In particular embodiments of the invention, a cytotoxin is an antibioticsuch as a calicheamicin, also called the LL-E33288 complex, for example,gamma-calicheamicin (γ₁) or N-acetyl gamma-calicheamicin. See U.S. Pat.No. 4,970,198. Additional examples of calicheamicins suitable for use inpreparing antibody/drug conjugates of the invention are disclosed inU.S. Pat. Nos. 4,671,958; 5,053,394; 5,037,651; 5,079,233; and5,108,912, which are incorporated herein in their entirety. Thesecompounds contain a methyltrisulfide that may be reacted withappropriate thiols to form disulfides, at the same time introducing afunctional group such as a hydrazide or other functional group that isuseful for conjugating calicheamicin to an anti-5T4 antibody. Disulfideanalogs of calicheamicin can also be used, for example, analogsdescribed in U.S. Pat. Nos. 5,606,040 and 5,770,710, which areincorporated herein in their entirety.

For radiotherapy applications, an anti-5T4 antibody of the invention maycomprise a high energy radioisotope. The isotope may be directly boundto the antibody, for example, at a cysteine residue present in theantibody, or a chelator may be used to mediate the binding of theantibody and the radioisotope. Radioisotopes suitable for radiotherapyinclude but are not limited to α-emitters, β-emitters, and augerelectrons. For diagnostic applications, useful radioisotopes includepositron emitters and γ-emitters. An anti-5T4 antibody of the inventionmay further be iodinated, for example, on a tyrosine residue of theantibody, to facilitate detection or therapeutic effect of the antibody.

Representative radioisotopes that may be conjugated to an anti-5T4antibody include ¹⁸-fluorine, ⁶⁴copper, ⁶⁵copper, ⁶⁷gallium, ⁶⁸gallium,⁷⁷bromine, ^(80m)bromine, ⁹⁵ruthenium, ⁹⁷ruthenium, ¹⁰³ruthenium,¹⁰⁵ruthenium, ^(99m)technetium, ¹⁰⁷mercury, mercury, ¹²³iodine,¹²⁴iodine, ¹²⁵iodine, 126iodine, ¹³¹iodine, ¹³³ iodine, ¹¹¹indium,¹¹³indium, ^(99m)rhenium, ¹⁰⁵rhenium, ¹⁰¹rhenium, ¹⁸⁶rhenium,¹⁸⁸rhenium, ¹²¹ mtellurium, ⁹⁹technetium, ^(122m)tellurium,^(125m)tellurium, ¹⁶⁵thulium, ¹⁶⁷thulium, ¹⁶⁸thulium, ⁹⁰yttrium, andnitride or oxide forms derived there from. Other suitable radioisotopesinclude alpha emitters, such as ²¹³bismuth, ²¹³lead, and ²²⁵actinium.

Antibody/drug conjugates of the invention may include immunomodulators,i.e., agents that elicit an immune response, including humoral immuneresponses (e.g. production of antigen-specific antibodies) andcell-mediated immune responses (e.g. lymphocyte proliferation).Representative immunomodulatory agents include cytokines, xanthines,interleukins, interferons, and growth factors (e.g., TNF, CSF, GM-CSFand G-CSF), and hormones such as estrogens (diethylstilbestrol,estradiol), androgens (testosterone, HALOTESTIN® (fluoxymesterone)),progestins (MEGACE® (megestrol acetate), PROVERA® (medroxyprogesteroneacetate)), and corticosteroids (prednisone, dexamethasone,hydrocortisone).

Immunomodulatory agents useful in the invention also includeanti-hormones that block hormone action on tumors and immunosuppressiveagents that suppress cytokine production, down-regulate self-antigenexpression, or mask MHC antigens. Representative anti-hormones includeanti-estrogens including, for example, tamoxifen, raloxifene, aromataseinhibiting 4(5)-imidazoles, 4-hydroxytamoxifen, trioxifene, keoxifene,LY 117018, onapnstone, and toremifene; and anti-androgens such asflutamide, nilutamide, bicalutamide, leuprolide, and goserelin; andanti-adrenal agents. Representative immunosuppressive agents include2-amino-6-aryl-5-substituted pyrimidines, azathioprine,cyclophosphamide, bromocryptine, danazol, dapsone, glutaraldehyde,anti-idiotypic antibodies for MHC antigens and MHC fragments,cyclosporin A, steroids such as glucocorticosteroids, cytokine orcytokine receptor antagonists (e.g., anti-interferon antibodies,anti-IL10 antibodies, anti-TNFα antibodies, anti-IL2 antibodies),streptokinase, TGFβ, rapamycin, T-cell receptor, T-cell receptorfragments, and T cell receptor antibodies.

Additional drugs useful in the invention include anti-angiogenic agentsthat inhibit blood vessel formation, for example, farnesyltransferaseinhibitors, COX-2 inhibitors, VEGF inhibitors, bFGF inhibitors, steroidsulphatase inhibitors (e.g., 2-methoxyoestradiol bis-sulphamate(2-MeOE2bisMATE)), interleukin-24, thrombospondin, metallospondinproteins, class I interferons, interleukin 12, protamine, angiostatin,laminin, endostatin, and prolactin fragments.

Anti-proliferative agents and pro-apoptotic agents include activators ofPPAR-gamma (e.g., cyclopentenone prostaglandins (cyPGs)), retinoids,triterpinoids (e.g., cycloartane, lupane, ursane, oleanane, friedelane,dammarane, cucurbitacin, and limonoid triterpenoids), inhibitors of EGFreceptor (e.g., HER4), rampamycin, CALCITRIOL®(1,25-dihydroxycholecalciferol (vitamin D)), aromatase inhibitors(FEMARA® (letrozone)), telomerase inhibitors, iron chelators (e.g.,3-aminopyridine-2-carboxaldehyde thiosemicarbazone (Triapine)), apoptin(viral protein 3-VP3 from chicken aneamia virus), inhibitors of Bcl-2and Bcl-X(L), TNF-alpha, FAS ligand, TNF-related apoptosis-inducingligand (TRAIL/Apo2L), activators of TNF-alpha/FAS ligand/TNF-relatedapoptosis-inducing ligand (TRAIL/Apo2L) signaling, and inhibitors ofPI3K-Akt survival pathway signaling (e.g., UCN-01 and geldanamycin).

Representative chemotherapeutic agents include alkylating agents such asthiotepa and cyclosphosphamide; alkyl sulfonates such as busulfan,improsulfan and piposulfan; aziidines such as benzodopa, carboquone,meturedopa, and uredopa; ethylenimines and methylamelamines includingaltretamine, triethylenemelamine, triethylenephosphoramide,triethylenethiophosphoramide and trimethylolomelamine; nitrogen mustardssuch as chlorambucil, chlornaphazine, cholophosphamide, estramustine,ifosfamide, mechiorethamine, mechiorethamine oxide hydrochloride,melphalan, novembichin, phenesterine, prednimustine, trofosfamide,uracil mustard; nitrosureas such as carmustine, chlorozotocin,fotemustine, lomustine, nimustine, ranimustine; antibiotics such asaclacinomysins, actinomycin, authramycin, azaserine, bleomycins,cactinomycin, calicheamicin, carabicin, caminomycin, carzinophilin,chromomycins, dactinomycin, daunorubicin, detorubicin,6-diazo-5-oxo-L-norleucine, doxorubicin, epirubicin, esorubicin,idarubicin, marcellomycin, mitomycins, mycophenolic acid, nogalamycin,olivomycins, peplomycin, potfiromycin, puromycin, quelamycin,rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex,zinostatin, zorubicin; anti-metabolites such as methotrexate and5-fluorouracil (5-FU); folic acid analogues such as denopterin,methotrexate, pteropterin, trimetrexate; purine analogs such asfludarabine, 6-mercaptopurine, thiamiprine, thioguanine; pyrimidineanalogs such as ancitabine, azacitidine, 6-azauridine, carmofur,cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine,5-EU; androgens such as calusterone, dromostanolone propionate,epitiostanol, mepitiostane, testolactone; anti-adrenal such asaminoglutethimide, mitotane, trilostane; folic acid replenisher such asfrolinic acid; aceglatone; aldophosphamide glycoside; aminolevulinicacid; amsacrine; bestrabucil; bisantrene; edatraxate; defofamine;demecolcine; diaziquone; elformithine; elliptinium acetate; etoglucid;gallium nitrate; hydroxyurea; lentinan; lonidamine; mitoguazone;mitoxantrone; mopidamol; nitracrine; pentostatin; phenamet; pirarubicin;podophyllinic acid; 2-ethylhydrazide; procarbazine; razoxane; sizofiran;spirogermanium; tenuazonic acid; triaziquone; 2, 2′,2′-trichlorotriethylamine; urethan; vindesine; dacarbazine;mannomustine; mitobronitol; mitolactol; pipobroman; gacytosine;arabinoside (Ara-C); cyclophosphamide; thiotepa; taxoids, e.g.paclitaxel (TAXOL®, Bristol-Myers Squibb Oncology of Princeton, N.J.)and doxetaxel (TAXOTERE®, Rhone-Poulenc Rorer of Antony, France);chlorambucil; gemcitabine; 6-thioguanine; mercaptopurine; methotrexate;platinum analogs such as cisplatin and carboplatin; vinblastine;platinum; etoposide (VP-16); ifosfamide; mitomycin C; mitoxantrone;vincristine; vinorelbine; navelbine; novantrone; teniposide; daunomycin;aminopterin; xeloda; ibandronate; CPT-11; topoisomerase inhibitor RFS2000; difluoromethylornithine (DMFO); retinoic acid; esperamicins; andcapecitabine.

Additional therapeutic agents that may be conjugated to anti-5T4antibodies and used in accordance with the therapeutic methods of thepresent invention include photosensitizing agents (U.S. PatentPublication No. 2002/0197262 and U.S. Pat. No. 5,952,329) forphotodynamic therapy; magnetic particles for thermotherapy (U.S. PatentPublication No. 2003/0032995); binding agents, such as peptides,ligands, cell adhesion ligands, etc., and prodrugs such asphosphate-containing prodrugs, thiophosphate-containing prodrugs,sulfate containing prodrugs, peptide containing prodrugs,β-lactam-containing prodrugs, substituted phenoxyacetamide-containingprodrugs or substituted phenylacetamide-containing prodrugs,5-fluorocytosine and other 5-fluorouridine prodrugs that may beconverted to the more active cytotoxic free drug.

For diagnostic methods using anti-5T4 antibodies, a drug may comprise adetectable label used to detect the presence of 5T4-expressing cells invitro or in vivo. Radioisotopes that are detectable in vivo, such asthose labels that are detectable using scintigraphy, magnetic resonanceimaging, or ultrasound, may be used in clinical diagnostic applications.Useful scintigraphic labels include positron emitters and γ-emitters.Representative contrast agents for magnetic source imaging areparamagnetic or superparamagnetic ions (e.g., iron, copper, manganese,chromium, erbium, europium, dysprosium, holmium and gadolinium), ironoxide particles, and water soluble contrast agents. For ultrasonicdetection, gases or liquids may be entrapped in porous inorganicparticles that are released as microbubble contrast agents. For in vitrodetection, useful detectable labels include fluorophores, detectableepitopes or binding agents, and radioactive labels.

III.B. Linker Molecules

Drugs are conjugated to chimeric and humanized anti-5T4 antibodies ofthe invention either directly or indirectly via a linker molecule. Thelinker molecule may be stable or hydrolyzable, whereby it is releasedfollowing cellular entry. The major mechanisms by which the drug iscleaved from the antibody include hydrolysis in the acidic pH of thelysosomes (hydrazones, acetals, and cis-aconitate-like amides), peptidecleavage by lysosomal enzymes (the cathepsins and other lysosomalenzymes), and reduction of disulfides. As a result of these varyingmechanisms for cleavage, mechanisms of linking the drug to the antibodyalso vary widely and any suitable linker can be used. Preferably, theconjugation method produces a sample with minimal low conjugate fraction(LCF, the fraction of mostly unconjugated antibody), i.e., less thanabout 10%.

One example of a suitable conjugation procedure relies on theconjugation of hydrazides and other nucleophiles to the aldehydesgenerated by oxidation of the carbohydrates that naturally occur onantibodies. Hydrazone-containing conjugates can be made with introducedcarbonyl groups that provide the desired drug-release properties.Conjugates can also be made with a linker that has a disulfide at oneend, an alkyl chain in the middle, and a hydrazine derivative at theother end. The anthracyclines are one example of cytotoxins that can beconjugated to antibodies using this technology.

Linkers containing functional groups other than hydrazones have thepotential to be cleaved in the acidic milieu of the lysosomes. Forexample, conjugates can be made from thiol-reactive linkers that containa site other than a hydrazone that is cleavable intracellularly, such asesters, amides, and acetals/ketals. Camptothecin is one cytotoxic agentthat can be conjugated using these linkers. Ketals made from a 5 to7-member ring ketone and that has one of the oxygens attached to thecytotoxic agent and the other to a linker for antibody attachment alsocan be used. The anthracyclines are also an example of a suitablecytotoxin for use with these linkers.

Another example of a class of pH sensitive linkers are thecis-aconitates, which have a carboxylic acid juxtaposed to an amidebond. The carboxylic acid accelerates amide hydrolysis in the acidiclysosomes. Linkers that achieve a similar type of hydrolysis rateacceleration with several other types of structures can also be used.The maytansinoids are an example of a cytotoxin that can be conjugatedwith linkers attached at C-9.

Another potential release method for drug conjugates is the enzymatichydrolysis of peptides by the lysosomal enzymes. In on example, apeptide is attached via an amide bond to para-aminobenzyl alcohol andthen a carbamate or carbonate is made between the benzyl alcohol and thecytotoxic agent. Cleavage of the peptide leads to the collapse, orself-immolation, of the aminobenzyl carbamate or carbonate. Thecytotoxic agents exemplified with this strategy include anthracyclines,taxanes, mitomycin C, and the auristatins. In one example, a phenol canalso be released by collapse of the linker instead of the carbamate. Inanother variation, disulfide reduction is used to initiate the collapseof a para-mercaptobenzyl carbamate or carbonate.

Many of the cytotoxic agents conjugated to antibodies have little, ifany, solubility in water and that can limit drug loading on theconjugate due to aggregation of the conjugate. One approach toovercoming this is to add solubilizing groups to the linker. Conjugatesmade with a linker consisting of PEG and a dipeptide can been used,including those having a PEG di-acid, thiol-acid, or maleimide-acidattached to the antibody, a dipeptide spacer, and an amide bond to theamine of an anthracycline or a duocarmycin analogue. Another example isa conjugate prepared with a PEG-containing linker disulfide bonded to acytotoxic agent and amide bonded to an antibody. Approaches thatincorporate PEG groups may be beneficial in overcoming aggregation andlimits in drug loading.

Representative linkers preferred for preparation of antibody/drugconjugates of the invention include linkers of the formula:(CO-Alk¹-Sp¹-Ar-Sp²-Alk²-C(Z¹)=Q-Sp)

wherein

Alk¹ and Alk² are independently a bond or branched or unbranched(C₁-C₁₀) alkylene chain;

Sp¹ is a bond, —S—, —O—, —CONH—, —NHCO—, —NR′—, —N(CH₂CH₂)₂N—, or—X—Ar′-Y—(CH₂)_(n)—Z wherein X, Y, and Z are independently a bond, —N′—,—S—, or —O—, with the proviso that when n=0, then at least one of Y andZ must be a bond and Ar′ is 1,2-, 1,3-, or 1,4-phenylene optionallysubstituted with one, two, or three groups of (C₁-C₅) alkyl, (C₁-C₄)alkoxy, (C₁-C₄) thioalkoxy, halogen, nitro, —COOR′, —CONHR′,—(CH₂)_(n)COOR′, —S(CH₂)_(n)COOR′, —O(CH₂)_(n)CONHR′, or—S(CH₂)_(n)CONHR′, with the proviso that when Alk¹ is a bond, Sp¹ is abond;

n is an integer from 0 to 5;

R′ is a branched or unbranched (C₁-C₅) chain optionally substituted byone or two groups of —OH, (C₁-C₄) alkoxy, (C₁-C₄) thioalkoxy, halogen,nitro, (C₁-C₃) dialkylamino, or (C₁-C₃) trialkylammonium-A⁻ where A⁻ isa pharmaceutically acceptable anion completing a salt;

Ar is 1,2-, 1,3-, or 1,4-phenylene optionally substituted with one, two,or three groups of (C₁-C₆) alkyl, (C₁-C₅) alkoxy, (C₁-C₄) thioalkoxy,halogen, nitro, —COOR′, —CONHR′, —O(CH₂)_(n)COOR′, —S(CH₂)_(n)COOR′,—O(CH₂)_(n)CONHR′, or —S(CH₂)_(n)CONHR′ wherein n and R′ are ashereinbefore defined or a 1,2-, 1,3-, 1,4-, 1,5-, 1,6-, 1,7-, 1,8-,2,3-, 2,6-, or 2,7-naphthylidene or

with each naphthylidene or phenothiazine optionally substituted withone, two, three, or four groups of (C₁-C₆) alkyl, (C₁-C₅) alkoxy,(C₁-C₄) thioalkoxy, halogen, nitro, —COOR′, —CONHR′, —O(CH₂)_(n)COOR′,—S(CH₂)_(n)COOR′, or —S(CH₂)_(n)CONHR′ wherein n and R′ are as definedabove, with the proviso that when Ar is phenothiazine, Sp¹ is a bondonly connected to nitrogen;

Sp² is a bond, —S—, or —O—, with the proviso that when Alk² is a bond,Sp² is a bond;

Z¹ is H, (C₁-C₅) alkyl, or phenyl optionally substituted with one, two,or three groups of (C₁-C₅) alkyl, (C₁-C₅) alkoxy, (C₁-C₄) thioalkoxy,halogen, nitro, —COOR′, —ONHR′, —O(CH₂)_(n)COOR′, —S(CH₂)_(n)COOR′,—O(CH₂)_(n)CONHR′, or —S(CH₂)_(n)CONHR′ wherein n and R′ are as definedabove;

Sp is a straight or branched-chain divalent or trivalent (C₁-C₁₈)radical, divalent or trivalent aryl or heteroaryl radical, divalent ortrivalent (C₃-C₁₈) cycloalkyl or heterocycloalkyl radical, divalent ortrivalent aryl- or heteroaryl-aryl (C₁-C₁₈) radical, divalent ortrivalent cycloalkyl- or heterocycloalkyl-alkyl (C₁-C₁₈) radical ordivalent or trivalent (C₂-C₁₈) unsaturated alkyl radical, whereinheteroaryl is preferably furyl, thienyl, N-methylpyrrolyl, pyridinyl,N-methylimidazolyl, oxazolyl, pyrimidinyl, quinolyl, isoquinolyl,N-methylcarbazoyl, aminocourmarinyl, or phenazinyl and wherein if Sp isa trivalent radical, Sp may be additionally substituted by lower (C₁-C₅)dialkylamino, lower (C₁-C₅) alkoxy, hydroxy, or lower (C₁-C₅) alkylthiogroups; and

Q is ═NHNCO—, ═NHNCS—, ═NHNCONH—, ═NHNCSNH—, or ═NHO—.

Preferably, Alk¹ is a branched or unbranched (C₁-C₁₀) alkylene chain;Sp′ is a bond, —S—, —O—, —CONH—, —NHCO—, or —NR′ wherein R′ is ashereinbefore defined, with the proviso that when Alk¹ is a bond, Sp¹ isa bond;

Ar is 1,2-, 1,3-, or 1,4-phenylene optionally substituted with one, two,or three groups of (C₁-C₆) alkyl, (C₁-C₅) alkoxy, (C₁-C₄) thioalkoxy,halogen, nitro, —COOR′, —CONHR′, —O(CH₂)_(n)COOR′, —S(CH₂)_(n)COOR′,—O(CH₂)_(n)CONHR′, or —S(CH₂)_(n)CONHR′ wherein n and R′ are ashereinbefore defined, or Ar is a 1,2-, 1,3-, 1,4-, 1,5-, 1,6-, 1,7-,1,8-, 2,3-, 2,6-, or 2,7-naphthylidene each optionally substituted withone, two, three, or four groups of (C₁-C₆) alkyl, (C₁-C₅) alkoxy,(C₁-C₄) thioalkoxy, halogen, nitro, —COOR′, —CONHR′, —O(CH₂)_(n)COOR′,—S(CH₂)_(n)COOR′, —O(CH₂)_(n)CONHR′, or —S(CH₂)_(n)CONHR′.

Z¹ is (C₁-C₅) alkyl, or phenyl optionally substituted with one, two, orthree groups of (C₁-C₅) alkyl, (C₁-C₄) alkoxy, (C₁-C₄) thioalkoxy,halogen, nitro, —COOR′, —CONHR′, —O(CH₂)_(n)COOR′, —S(CH₂)_(n)COOR′,—O(CH₂)_(n)CONHR′, or —S(CH₂)_(n)CONHR′; Alk² and Sp² are together abond; and Sp and Q are as immediately defined above.

U.S. Pat. No. 5,773,001, incorporated herein in its entirety, discloseslinkers that may be used with nucleophilic drugs, particularlyhydrazides and related nucleophiles, prepared from the calicheamicins.These linkers are especially useful in those cases where better activityis obtained when the linkage formed between the drug and the linker ishydrolyzable. These linkers contain two functional groups, including (1)a group for reaction with an antibody (e.g., carboxylic acid), and (2) acarbonyl group (e.g., an aldehyde or a ketone) for reaction with a drug.The carbonyl groups may react with a hydrazide group on the drug to forma hydrazone linkage. This linkage is hydrolyzable, allowing for releaseof the therapeutic agent from the conjugate after binding to the targetcells.

As one example, an anti-5T4 antibody may be conjugated to a cytotoxicdrug by (1) adding the cytotoxic drug derivative to the anti-5T4antibody wherein the cytotoxic drug is 4.5%-11% by weight of theproteinaceous carrier; (2) incubating the cytotoxic drug derivative andanti-5T4 antibody in a non-nucleophilic, protein-compatible, bufferedsolution having a pH in the range from about 7 to 9 to produce amonomeric cytotoxic drug/antibody conjugate, wherein the solutionfurther comprises (a) a suitable organic cosolvent, and (b) an additivecomprising at least one C₆-C₁₈ carboxylic acid or its salt, and whereinthe incubation is conducted at a temperature ranging from about 30° C.to about 35° C. for a period of time ranging from about 15 minutes to 24hours; and (3) subjecting the conjugate produced in step (2) to achromatographic separation process to separate monomeric conjugates witha loading in the range of 3% to 10% by weight cytotoxic drug and withlow conjugated fraction (LCF) below 10 percent from unconjugatedantibody, cytotoxic drug derivative, and aggregated conjugates.

The chromatographic separation of step (3) can include processes such assize exclusion chromatography (SEC), ultrafiltration/diafiltration,HPLC, FPLC, or Sephacryl S-200 chromatography. The chromatographicseparation may also be accomplished by hydrophobic interactionchromatography (HIC) using Phenyl Sepharose 6 Fast Flow chromatographicmedium, Butyl Sepharose 4 Fast Flow chromatographic medium, OctylSepharose 4 Fast Flow chromatographic medium, Toyopearl Ether-650Mchromatographic medium, Macro-Prep methyl HIC medium or Macro-Prept-Butyl HIC medium.

Representative methods for preparing anti-5T4 antibody/drug conjugatesinclude those described for preparation of CMC-544 in co-pendingpublished U.S. Patent Application Publication No. 2004-082764A1 and U.S.patent application Ser. No. 10/699,874, which are incorporated herein intheir entirety. Conjugation may be performed using the followingconditions: 10 mg/ml antibody, 8.5% (w/w) calicheamicin derivative, 37.5mM sodium decanoate, 9% (v/v) ethanol, 50 mM HEPES(N-(2-Hydroxyethyl)piperazine-N′-(4-butanesulfonic acid)), pH 8.5, 32°C., 1 hour. Hydrophobic interaction chromatography (HIC) may beperformed using a butyl sepharose FF resin, 0.65 M potassium phosphateloading buffer, 0.49 M potassium phosphate wash buffer, and 4 mMpotassium phosphate elution buffer. Buffer exchange may be accomplishedby size exclusion chromatography, ultrafiltration/diafiltration, orother suitable means. The antibody/drug conjugate may be formulated in1.5% Dextran-40, 0.9% sucrose, 0.01% TWEEN®-80, 20 mM Tris/50 mM NaCl,pH 8.0. An alternative formulation solution containing 5% sucrose, 0.01%TWEEN®-80, 20 mM Tris/10 mM NaCl, pH 8.0 may also be used.Lyophilization cycles are adjusted based on the formulation. Theconcentration of the formulated bulk may be 0.5 mg conjugate/ml. Eachmay vial contain 1 mg of conjugate, i.e., 2 ml fill. Other fill volumesmay be prepared as desired, e.g., 5 ml fill.

Other representative methods include those described for CMD-193, alsodescribed in U.S. Patent Application Publication No. 20060002942.Conjugation may be performed using the following conditions: 10 mg/mlantibody, 7% (w/w) calicheamicin derivative, 10 mM deoxycholate, 50 mMHEPBS (N-(2-Hydroxyethyl)piperazine-N′-(4-butanesulfonic acid)), 9%(v/v) ethanol, pH 8.2, 32° C., 1 hour. The reaction may be diluted10-fold with 0.66 M potassium phosphate pH 8.56, and HIC may beperformed using a butyl sepharose FF resin, 0.60 M potassium phosphateloading buffer and wash buffer, and 20 mM Tris/25 mM NaCl elutionbuffer. Buffer exchange may be accomplished usingultrafiltration/diafiltration with a regenerated cellulose membrane. Theconjugate may be diafiltered against 20 mM Tris/10 mM NaCl pH 8.0 (10diavolumes). The antibody/drug conjugate may be formulated in 5%sucrose, 0.01% TWEEN®-80, 20 mM Tris/10 mM NaCl, pH 8.0. Theconcentration of the bulk conjugate after formulation may be 1 mg/ml,and the vial fill may be 5 mg/vial, i.e., 5 ml fill, or other fillvolumes may be prepared as desired.

In a particular embodiment of the invention, the linker employed is4-(4-acetylphenoxy) butanoic acid (AcBut). Antibody/drug conjugates areprepared by reacting β-calicheamicin, γ-calicheamicin or N-acetylγ-calicheamicin, or derivatives thereof, with 3-mercapto-3-methylbutanoyl hydrazide, the AcBut linker, and an anti-5T4 antibody of theinvention. See e.g., U.S. Pat. No. 5,773,001. This linker producesconjugates that are substantially stable in circulation, releasing anestimated 2% of the NAc-gamma DMH per day, and which release theNAc-gamma DMH readily in the acidic lysosomes. In other embodiments ofthe invention, antibody/drug conjugates are prepared using3-acetylphenyl acidic acid (AcPac) or 4-mercapto-4-methyl-pentanoic acid(Amide) as the linker molecule.

Representative linkers useful for conjugation of radioisotopes includediethylenetriamine pentaacetate (DTPA)-isothiocyanate, succinimidyl6-hydrazinium nicotinate hydrochloride (SHNH), and hexamethylpropyleneamine oxime (HMPAO) (Bakker et al. (1990) J. Nucl. Med. 31: 1501-1509,Chattopadhyay et al. (2001) Nucl. Med. Biol. 28: 741-744, Dewanjee etal. (1994) J. Nucl. Med. 35: 1054-63, Krenning et al. (1989) Lancet 1:242-244, Sagiuchi et al. (2001) Ann. Nucl. Med. 15: 267-270); U.S. Pat.No. 6,024,938). Alternatively, a targeting molecule may be derivatizedso that a radioisotope may be bound directly to it (Yoo et al. (1997) J.Nucl. Med. 38: 294-300). Iodination methods are also known in the art,and representative protocols may be found, for example, in Krenning etal. (1989) Lancet 1:242-4 and in Bakker et al. (1990) J. Nucl. Med.31:1501-9.

To further increase the number of drug molecules per antibody/drugconjugate, the drug may be conjugated to polyethylene glycol (PEG),including straight or branched polyethylene glycol polymers andmonomers. A PEG monomer is of the formula: —(CH₂CH₂O)—. Drugs and/orpeptide analogs may be bound to PEG directly or indirectly, i.e. throughappropriate spacer groups such as sugars. A PEG/antibody/drugcomposition may also include additional lipophilic and/or hydrophilicmoieties to facilitate drug stability and delivery to a target site invivo. Representative methods for preparing PEG-containing compositionsmay be found in U.S. Pat. Nos. 6,461,603; 6,309,633; and 5,648,095,among other places.

For example, to increase the amount of calicheamicin inantibody-calicheamicin conjugates, the antibody is conjugated to PEGprior to conjugation with calicheamicin, for example, using PEG-SPA,PEG-SBA, or PEG-bis-maleimide. Antibody/drug conjugates prepared usingPEG may show reduced binding affinity for the target antigen, but arestill effective as a result of increased drug load. Additives such asdeoxycholate and decanoate may be used to produce anantibody/calicheamicin conjugates with low levels of unconjugatedantibody and low levels of aggregate.

The hydrophobic nature of many drugs, including calicheamicins, mayresults in aggregation of antibody/drug conjugates. To produce monomericantibody/drug conjugates with higher drug loading/yield and decreasedaggregation, the conjugation reaction may be performed in anon-nucleophilic, protein-compatible, buffered solution containing (i)propylene glycol as a cosolvent and (ii) an additive comprising at leastone C₆-C₁₈ carboxylic acid. Useful acids include C₇ to C₁₂ acids, suchas octanoic acid or caprylic acid, or its salts. Otherprotein-compatible organic cosolvents other than propylene glycol, suchas ethylene glycol, ethanol, DMF, DMSO, etc., may also be used. Some orall of the organic cosolvent is used to transfer the drug into theconjugation mixture. Useful buffers for the preparation of antibody/drugconjugates using N-hydroxysuccinimide (OSu) esters or other comparablyactivated esters include phosphate-buffered saline (PBS) andN-2-hydroxyethyl piperazine-N′-2-ethanesulfonic acid (HEPES buffer). Thebuffered solution used in conjugation reactions should substantiallylack free amines and nucleophiles. As another approach, the conjugationreactions may be performed in a non-nucleophilic, protein-compatible,buffered solution containing t-butanol without the additional additives.See e.g., U.S. Pat. Nos. 5,712,374 and 5,714,586. Additional methods forconjugation and calicheamicin-containing conjugates are described inU.S. Pat. Nos. 5,739,116 and 5,877,296.

Optimal reaction conditions for formation of a monomeric conjugate maybe empirically determined by variation of reaction variables such astemperature, pH, calicheamicin derivative input, and additiveconcentration. Representative amounts of propylene glycol range from 10%to 60%, for example, 10% to 40%, or about 30% by volume of the totalsolution. Representative amounts of an additive comprising at least oneC₆-C₁₈ carboxylic acid or its salt range from 20 mM to 100 mM, such asfrom 40 mM to 90 mM, or about 60 mM to 90 mM. The concentration of theC₆-C₁₈ carboxylic acid or its salt may be increased to 150-300 mM andthe cosolvent dropped to 1% to 10%. In representative embodiments of theinvention, the carboxylic acid is octanoic acid, decanoic acid, or thecorresponding salts. For example, 200 mM caprylic acid may be used with5% propylene glycol or ethanol. The conjugation reaction may beperformed at slightly elevated temperature (30-35° C.) and pH (8.2-8.7).The concentration of antibody may range from 1 to 15 mg/ml and theconcentration of a calicheamicin derivative, e.g., N-Acetylgamma-calicheamicin DMH AcBut OSu ester may range from about 4.5% to 11%by weight of the antibody. Conditions suitable for conjugation of otherdrugs may be determined by those skilled in the art without undueexperimentation.

III.C. Purification of Antibody/Drug Conjugates

Following conjugation, the monomeric conjugates may be separated fromunconjugated reactants and/or aggregated forms of the conjugates byconventional methods, for example, size exclusion chromatography (SEC),hydrophobic interaction chromatography (HIC), ion exchangechromatography (IEC), or chromatofocusing (CF). The purified conjugatesare monomeric, and usually contain from 3% to 10% drug by weight.Antibody/drug conjugates may also be purified using hydrophobicinteraction chromatography (HIC), which offers some advantages over SECincluding (1) a capability to efficiently reduce the LCF content as wellas aggregate; (2) accommodation of large reaction volumes; and (3)minimal dilution of the product. High-capacity HIC media suitable forproduction scale use include Phenyl Sepharose 6 Fast Flowchromatographic medium, Butyl Sepharose 4 Fast Flow chromatographicmedium, Octyl Sepharose 4 Fast Flow chromatographic medium, ToyopearlEther-650M chromatographic medium, Macro-Prep methyl HIC medium orMacro-Prep t-Butyl HIC medium. Ultrafiltration/diafiltration may also beused for buffer exchange.

In a representative purification process, multiple steps are performed,including a centrifuge cell removal step, a Protein A affinity capturestep followed by one or two orthogonal chromatographic polishing steps,a virus filtration step, and a tangential flow filtration step forconcentration and formulation. The purification process preferablyyields product with less than 5% aggregate, less than 20 ppm Protein A,less than 50 ppm host cell protein, and overall recovery of greater than50%.

A typical anti-5T4/calicheamicin preparation contains predominantly(˜95%) conjugated antibody containing 5-7 moles calicheamicin per moleantibody. The conjugate has been reproducibly prepared at the laboratoryscale (10-200 mg). Drug loading, which is expressed as μgcalicheamicin/mg monoclonal antibody, is determined by dividing thecalicheamicin concentration (μg/mL) by the antibody concentration(mg/mL). These values are determined by measuring the UV absorbance ofthe conjugate solution at 280 nm and 310 nm. It is important to notethat this is an average loading and that the actual loading is aquasi-gaussian distribution centered on the average loading value, i.e.,some of the antibody is loaded higher than average and some of theantibody is loaded lower than the average. Unconjugated antibody (lowconjugated fraction), which can be measured using analytical HIC-HPLC(hydrophobic interaction high-performance liquid chromatography), is thepopulation of antibody that has little or no conjugated calicheamicin.This value is a measure of calicheamicin distribution on the antibodyand does not generally affect the amount of calicheamicin dosed.Unconjugated calicheamicin, which can be measured using ELISA, refers tothe amount of calicheamicin that is not conjugated to the antibody andis expressed in terms of percent of total calicheamicin. Drug-loadingassays do not differentiate between unconjugated and conjugatedcalicheamicin. The amount of unconjugated calicheamicin is undetectableor negligible when using drug-loading assays, and therefore these assayseffectively measure the amount of conjugated calicheamicin.

Analytical methods can be used to assay for release and stabilitytesting of humanized anti-5T4 calicheamicin conjugates. The conjugatescan be evaluated for identity (IEF), strength (total protein and totalcalicheamicin loading), purity (unconjugated calicheamicin, lowconjugated antibody, aggregate content and SDS-PAGE Reduced), andimmunoaffinity (antigen binding ELISA). Additional assays known to thoseof skill in the art can be used. Using these assays, batch-to-batchconsistency can be maintained in commercial manufacture.

III.D. Pharmacokinetics of Antibody/Drug Conjugates

The pharmacokinetics of 5T4-targeted immunoconjugates can be evaluatedand compared to the pharmacokinetics of unconjugated calicheamicin invarious animals. For example, this can be done following a singleintravenous bolus administration in female nude mice, maleSprague-Dawley rats, and female cynomologus monkeys. Pharmacokinetics ofan anti-5T4 antibody are generally characterized by low clearance, lowvolume of distribution, and long apparent terminal half-life in variousspecies. The serum concentrations of unconjugated calicheamicinderivatives are expected to be below the quantification limit. Thetoxicity profile for these conjugates in single-dose toxicity rangingstudies is expected to be similar to that obtained for otherantibody/calicheamicin conjugates at comparable doses.

IV. Functional Assays for Characterization of Anti-5T4 Antibodies andAntibody/Drug Conjugates

The present invention further discloses in vitro and in vivo assays tocharacterize activities of an anti-5T4 antibody, including 5T4 bindingactivity, cellular internalization following binding to 5T4 antigenpresented on a cell surface, and targeting to 5T4-expressing cells in asubject. When conjugated to a cytotoxin, the disclosed antibodies of theinvention may elicit anti-cancer activity, including inhibition ofgrowth of 5T4-expressing cancer cells and/or induction of cell death in5T4-expressing cells. Anti-5T4 antibodies of the invention may compriseone or more of the foregoing activities.

Techniques for detecting binding of anti-5T4 antibodies to 5T4 antigenare known in the art, including for example, BIACORE® assays asdescribed in Example 2. Additional representative techniques includecentrifugation, affinity chromatography and other immunochemicalmethods. See e.g., Manson (1992) Immunochemical Protocols, Humana Press,Totowa, N.J., United States of America; Ishikawa (1999) Ultrasensitiveand Rapid Enzyme Immunoassay, Elsevier, Amsterdam/New York. Antigenbinding assays may be performed using isolated 5T4 antigen or5T4-expressing cells. See Example 2.

The binding specificity of anti-5T4 antibodies may be further describedby definition of a binding epitope, i.e., identification of residues,including nonadjacent residues that participate in antigen binding,and/or definition of residues that influence antigen binding. SeeExamples 4-5.

Internalization of anti-5T4 antibodies and antibody/drug conjugates by5T4-expressing cells may be assayed by observing the amount ofantibodies or conjugates bound to the surface of the 5T4-expressingcells over time. Representative techniques for assessing membranelocalization of antibodies and antibody/drug conjugates are described inExample 3.

Functional assays also include methods for assessing anti-canceractivity of antibody/drug conjugates, for example, an ability to destroyexisting cancer cells, or to delay or prevent growth of cancer cells.Cancers targeted by antibody/drug conjugates of the invention includeboth primary and metastasized tumors and carcinomas of any tissue in asubject, including carcinomas and hematopoietic malignancies such asleukemias and lymphomas.

Anti-5T4 antibodies having growth inhibitory activity can eliminate5T4-expressing cells or to prevent or reduce proliferation of5T4-expressing cells. Representative methods for rapid in vitroassessment of cell growth inhibition are described in Jones et al.(2001) J. Immunol. Methods 254:85-98.

Anti-5T4 antibodies may also comprise an ability to induce cell death,for example, programmed cell death characterized by nuclear DNAdegradation, nuclear degeneration and condensation, loss of membraneintegrity, and phagocytosis. Representative assays to assess cell aredescribed in Hoves et al. (2003) Methods 31:127-34; Peng et al. (2002)Chin. Med. Sci. J. 17:17-21; Yasuhara et al. (2003) J. Histochem.Cytochem. 51:873-885.

For example, to assess the cytotoxicity of anti-5T4antibody/calicheamicin conjugates in vitro, MDAMB435/5T4 cells (humanbreast carcinoma cells overexpressing human 5T4 antigen) andMDAMB435/neo cells (control cells) are cultured in the presence ofantibody-calicheamicin conjugates or free calicheamicin, essentially asdescribed by Boghaert et al. (2004), Clin. Cancer Res., 10: 4538-4549.The cytotoxicity of each agent is reported as ED50 (ng/ml), which is theamount of calicheamicin given as conjugate or as free drug that causes50% reduction of a cell culture relative to an untreated control. Thenumber of cells in culture is determined using a vital dye (MTS)following drug exposure. See also Example 6.

The cytotoxicity of antibody/calicheamicin conjugates may also beassessed using MDAMB435/5T4 and MDAMB435/neo cells cultured in a mannersuitable for spheroid growth. Cells are cultured in the presence ofantibody/calicheamicin conjugates or free calicheamicin, and followingdrug exposure, the dimensions of each spheroid was determined. Theefficiency of each of agent in inhibiting spheroid growth is reported asED50 (ng/ml), i.e., the amount of calicheamicin given as conjugate or asfree drug that causes 50% inhibition of spheroid growth relative to anuntreated control. See Example 6.

To assess the cytotoxicity of anti-5T4 antibody/calicheamicin conjugatesin vivo, tumors are prepared in nude mice by subcutaneous injection ofMDAMB435/5T4 cells (human breast carcinoma cells overexpressing human5T4 antigen), NCI-H157 cells (human non-small cell lung cancer cells),PC14PE6 cells (human non-small cell lung cancer cells), or N87 cells(human gastric carcinoma cells). Antibody/calicheamicin conjugates andcontrol compounds are administered to tumor-bearing mice, for example,by intraperitoneal injection in a total of 3 doses given at 4-dayintervals, e.g., on days 1, 5, and 9. Measurable therapeutic outcomesinclude inhibition of tumor cell growth.

To further assess the targeting ability of anti-5T4antibody/calicheamicin conjugates, an orthotopic model for non-smallcell and small cell cancer may be used, essentially as described by Onnet al. (2003) Clin. Cancer Res. 9(15):5532-5539. In brief, human lungadenocarcinoma (PC14PE6) cells are injected into tail veins of nudemice, which then migrate to form tumors in lung. Tumors may appear assolid nodules in the lung parenchyma and cause hemorrhagic pleuraleffusions containing suspended tumor cells. Control compounds andantibody/calicheamicin conjugates are administered to tumor-bearingmice, for example, by intraperitoneal injection beginning at 6 daysafter injection of tumor cells for a total of 3 doses given at 4-dayintervals, e.g., on days 6, 10, and 14. Measurable therapeutic outcomesinclude reduced pleural effusions and increased survival.

V. Uses of Anti-5T4 Antibodies and Antibody/Drug Conjugates

The anti-5T4 antibodies and antibody/drug conjugates of the inventionare useful both in vitro and in vivo for applications related to5T4-expressing cells. Cancers expressing 5T4 includesquamous/adenomatous lung carcinoma (non-small-cell lung carcinoma),invasive breast carcinoma, colorectal carcinoma, gastric carcinoma,squamous cervical carcinoma, invasive endometrial adenocarcinoma,invasive pancreas carcinoma, ovarian carcinoma, squamous vesicalcarcinoma, and choriocarcinoma. 5T4 is detected at high levels oncarcinomas of bronchi, breast, colon, rectum, stomach, cervix,endometrium, pancreas, ovaria, chorium, and seminal vesicles.

V.A. In Vitro Applications

The present invention provides in vitro methods using anti-5T4antibodies. For example, the disclosed antibodies may be used, eitheralone or in combination with cytotoxic agents or other drugs tospecifically bind 5T4-positive cancer cells to deplete such cells from acell sample. Methods are also provided for inducing apoptosis and/orinhibition of cell proliferation via contacting 5T4-expressing cellswith an antibody/drug conjugate comprising an anti-5T4 antibodyconjugated to a cytotoxin. Representative in vitro methods are describedherein above under the heading of “Functional Assays forCharacterization of Anti-5T4 Antibodies and Antibody/Drug Conjugates.”

Anti-5T4 antibodies of the invention also have utility in the detectionof 5T4-positive cells in vitro based on their ability to specificallybind 5T4 antigen. A method for detecting 5T4-expressing cells maycomprise: (a) preparing a biological sample comprising cells; (b)contacting an anti-5T4 antibody with the biological sample in vitro; and(c) detecting binding of anti-5T4 antibody. To facilitate detection, theantibody may be conjugated to a label.

V.B. In Vivo Detection and Diagnosis

Anti-5T4 antibodies of the invention may also be used for in vivodetection methods, for example, as useful for diagnosis, to provideintraoperative assistance, or for dose determination. Followingadministration of a labeled anti-5T4 antibody to a subject, and after atime sufficient for binding, the biodistribution of 5T4-expressing cellsbound by the antibody may be visualized. The disclosed diagnosticmethods may be used in combination with treatment methods. In addition,anti-5T4 antibodies of the invention may be administered for the dualpurpose of detection and therapy.

Representative non-invasive detection methods include scintigraphy(e.g., SPECT (Single Photon Emission Computed Tomography), PET (PositronEmission Tomography), gamma camera imaging, and rectilinear scanning),magnetic resonance imaging (e.g., convention magnetic resonance imaging,magnetization transfer imaging (MTI), proton magnetic resonancespectroscopy (MRS), diffusion-weighted imaging (DWI) and functional MRimaging (fMRI)), and ultrasound.

V.C. Therapeutic Applications

The present invention further relates to methods and compositions usefulfor inducing cytolysis of 5T4-expressing cancer cells in a subject. Theanti-5T4 antibody/drug conjugates of the invention are useful forinhibiting growth of cancerous cells and cells of a non-neoplasticproliferative disorder, such as hyperplasia, metaplasia, or mostparticularly, dysplasia (for review of such abnormal growth conditions,see DeVita, Jr. et al. (2001), Cancer: Principles and Practice, 6^(th)edition, Lippincott Williams & Wilkins.

Cancers suitable for targeting using anti-5T4 antibody/drug conjugatesinclude 5T4-expressing primary and metastatic tumors in breast, colon,rectum, lung, oropharynx, hypopharynx, esophagus, stomach, pancreas,liver, gallbladder, bile ducts, small intestine, urinary tract includingkidney, bladder and urothelium, female genital tract, cervix, uterus,ovaries, male genital tract, prostate, seminal vesicles, testes, anendocrine gland, thyroid gland, adrenal gland, pituitary gland, skin,bone, soft tissues, blood vessels, brain, nerves, eyes, meninges. Otherrelevant cancers are 5T4-expressing leukemias and lymphomas (e.g.,Hodgkin's lymphoma and non-Hodgkin's lymphoma), including indolent,aggressive, low-grade, intermediate-grade, or high-grade leukemia orlymphoma.

In particular, 5T4 is known to be expressed on cells ofsquamous/adenomatous lung carcinoma (non-small-cell lung carcinoma),invasive breast carcinoma, colorectal carcinoma, gastric carcinoma,squamous cervical carcinoma, invasive endometrial adenocarcinoma,invasive pancreas carcinoma, ovarian carcinoma, squamous vesicalcarcinoma, and choriocarcinoma. 5T4 is detected at high levels oncarcinomas of bronchi, breast, colon, rectum, stomach, cervix,endometrium, pancreas, ovaria, chorium and seminal vesicles. The cellsurface distribution of the 5T4 antigen may be homogeneous orheterogeneous. In colorectal carcinoma, gastric carcinoma, and ovariancarcinoma, expression of 5T4 is directly related to progression of thedisease. In breast carcinoma, increased intensity of 5T4 staining onmetastatic nodules is observed, however, 5T4 expression is notcorrelated with disease stage. The cancers may also express the Lewis Ycarbohydrate antigen, including breast, colon, gastric, esophageal,pancreatic, duodenal, lung, bladder and renal carcinomas and gastric andislet cell neuroendocrine tumors. See U.S. Pat. No. 6,310,185.

Thus, patients to be treated with the anti-5T4/drug conjugates of theinvention may be selected based on biomarker expression, including butnot limited to elevated expression of 5T4 antigen, resulting in apatient population selected for enriched target expression rather thantumor origin or histology. Target expression can be measured as afunction of the number of cells staining combined with the intensity ofthe cells staining. For example, classification of high expression of5T4 includes those patients with greater than 30% (i.e., 40%, 50% or60%) of the cells tested by immunohistochemical staining positive for5T4 at a level of 3+ (on a scale of 1 to 4), while moderate expressionof the 5T4 can include those patients with greater than 20% of the cellcells staining at 1+ to 2+.

Biomarkers other than expression of 5T4 antigen can be also used forpatient selection, including characterization of the tumor based onmulti-drug resistance (MDR), for example. Nearly 50 percent of humancancers are either completely resistant to chemotherapy or respond onlytransiently, after which they are no longer affected by commonly usedanticancer drugs. This phenomenon is referred to as MDR and isinherently expressed by some tumor types, while others acquire MDR afterexposure to chemotherapy treatment. The drug efflux pump P-glycoproteinmediates a majority of the MDR associated with cytotoxicchemotherapeutics. Phenotypic and functional analysis of MDR mechanismspresent in cancer patient tumor specimens can be conducted in order torelate specific MDR mechanism(s) with resistance to chemotherapy inspecific tumor types.

Cancer growth or abnormal proliferation refers to any one of a number ofindices that suggest change within cells to a more developed cancer formor disease state. Inhibition of growth of cancer cells or cells of anon-neoplastic proliferative disorder may be assayed by methods known inthe art, such as delayed tumor growth and inhibition of metastasis.Other indices for measuring inhibition of cancer growth include adecrease in cancer cell survival, a decrease in tumor volume ormorphology (for example, as determined using computed tomographic (CT),sonography, or other imaging method), destruction of tumor vasculature,improved performance in delayed hypersensitivity skin test, an increasein the activity of cytolytic T-lymphocytes, and a decrease in levels oftumor-specific antigens.

While not intending to be bound by any single mode of operation, bothantigen-guided targeting as well as passive targeting of anti-5T4antibody/drug conjugates may contribute to anti-tumor efficacy.Antigen-guided targeting refers to the preferential movement and/oraccumulation of a peptide or peptide analog in a target tissue (i.e., atissue comprising 5T4-expressing cells and intended site foraccumulation of an anti-5T4/drug conjugate) as compared with a controltissue (i.e., a tissue suspected to substantially lack 5T4-expressingcells and binding and/or accumulation of an administered anti-5T4/drugconjugate). Preferential localization of an antibody/drug conjugate isgenerally such that an amount of antibody/drug conjugate in a targettissue is about 2-fold greater than an amount of antibody/drug conjugatein a control tissue, such as an amount that is about 5-fold or greater,or about 10-fold or greater.

Passive targeting generally refers to sequestering of antibodies orantibody/drug conjugates at a tumor site due to local changes invasculature. For example, anti-5T4/drug conjugates may leave thevasculature at the tumor site, which is fenestrated due to increasedVEGF production, bind to 5T4-expressing cells and triggerinternalization of the anti-5T4/drug conjugate. Poor venous andlymphatic drainage of the tumor also result in sequestration of unboundanti-5T4/drug conjugates. Antibodies conjugated to drugs with acidlabile linkers can release the drug, which then diffuses into tumorcells. The anti-tumor effects of passive targeting are not permanent oras potent as those induced by antigen-guided targeting, but maycontribute to total efficacy.

V.D. Formulations

Anti-5T4 antibodies and anti-5T4/drug conjugates of the invention arereadily prepared and formulated for safe and efficacious clinical use.Suitable formulations for administration to a subject include aqueousand non-aqueous sterile injection solutions which may containanti-oxidants, buffers, bacteriostats, antibacterial and antifungalagents (e.g., parabens, chlorobutanol, phenol, ascorbic acid, andthimerosal), solutes that render the formulation isotonic with thebodily fluids of the intended recipient (e.g., sugars, salts, andpolyalcohols), suspending agents and thickening agents. Suitablesolvents include water, ethanol, polyol (e.g., glycerol, propyleneglycol, and liquid polyethylene glycol), and mixtures thereof. Theformulations may be presented in unit-dose or multi-dose containers, forexample, sealed ampoules and vials, and may be stored in a frozen orfreeze-dried (lyophilized) condition requiring only the addition ofsterile liquid carrier immediately prior to use for administration to asubject or for subsequent radiolabeling with an isotope appropriate forthe intended application. Anti-5T4 antibodies and antibody/drugconjugates of the invention are preferably formulated as an effectivedose, described below.

As one example, a representative anti-5T4 antibody or anti-5T4/drugconjugate formulation comprises a multi-dose formulation of 40 mg/mlantibody or antibody/drug conjugate, 25 mM acetate, 150 mM trehalose,0.9% benzyl alcohol, 0.02% polysorbate 20 at pH 5.0, and which has aminimum shelf life of two years storage at 2-8° C. As another example,an anti-5T4 antibody or anti-5T4/drug conjugate formulation may comprise10 mg/ml antibody or antibody/drug conjugate in 9.0 mg/ml sodiumchloride, 7.35 mg/ml sodium citrate dihydrate, 0.7 mg/ml polysorbate 80,and sterile water, pH 6.5. Representative formulations of ananti-5T4/calicheamicin conjugate for administration to experimentalmouse models include 2 μg or 4 μg calicheamicin (see Examples 3, 4, and7), which may be scaled accordingly for administration to humans.

A stable lyophilized formulation of an anti-5T4 antibody orantibody/drug conjugate may be prepared by (a) dissolving anantibody/drug conjugate to a final concentration of 0.5 to 2 mg/ml in asolution comprising a cryoprotectant at a concentration of 1.5%-5% byweight, a polymeric bulking agent at a concentration of 0.5-1.5% byweight, electrolytes at a concentration 0.01 M to 0.1 M, a solubilityfacilitating agent at a concentration of 0.005% to 0.05% by weight,buffering agent at a concentration of 5-50 mM such that the final pH ofthe solution is 7.8-8.2, and water; (b) dispensing the above solutioninto vials at a temperature of +5° C. to +10° C.; (c) freezing thesolution at a freezing temperature of −35° C. to −50° C.; (d) subjectingthe frozen solution to an initial freeze drying step at a primary dryingpressure of 20 to 80 microns at a shelf temperature at −10° C. to −40°C. for 24 to 78 hours; and (e) subjecting the freeze-dried product ofstep (d) to a secondary drying step at a drying pressure of 20 to 80microns at a shelf temperature of +10° C. to +35° C. for 15 to 30 hours.

Representative cryoprotectants useful for lyophilization of thecryoprotectant include alditol, mannitol, sorbitol, inositol,polyethylene glycol, aldonic acid, uronic acid, aldaric acid, aldoses,ketoses, amino sugars, alditols, inositols, glyceraldehydes, arabinose,lyxose, pentose, ribose, xylose, galactose, glucose, hexose, idose,mannose, talose, heptose, glucose, fructose, gluconic acid, sorbitol,lactose, mannitol, methyl α-glucopyranoside, maltose, isoascorbic acid,ascorbic acid, lactone, sorbose, glucaric acid, erythrose, threose,arabinose, allose, altrose, gulose, idose, talose, erythrulose,ribulose, xylulose, psicose, tagatose, glucuronic acid, gluconic acid,glucaric acid, galacturonic acid, mannuronic acid, glucosamine,galactosamine, sucrose, trehalose, neuraminic acid, arabinans, fructans,fucans, galactans, galacturonans, glucans, mannans, xylans, levan,fucoidan, carrageenan, galactocarolose, pectins, pectic acids, amylose,pullulan, glycogen, amylopectin, cellulose, dextran, pustulan, chitin,agarose, keratin, chondroitin, dermatan, hyaluronic acid, alginic acid,xanthan gum, starch, sucrose, glucose, lactose, trehalose, ethyleneglycol, polyethylene glycol, polypropylene glycol, glycerol andpentaerythritol.

For example, the cryoprotectant sucrose may be used at a concentrationof 1.5% by weight, the polymeric bulking agent Dextran 40 orhydroxyethyl starch 40 may be used at a concentration of 0.9% by weight,the electrolyte used in the lyophilization solution is sodium chloride,which is present at a concentration of 0.05 M, and the buffering agenttromethamine may be used at a concentration of 0.02 M. A solubilityfacilitating agent (e.g., a surfactant such as Polysorbate 80) may alsobe used during the lyophilization process. Usually this solubilityfacilitating agent is a surfactant. Representative steps for preparationof a lyophilized formulation include freezing the vials at a temperatureof −45° C.; the frozen solution is subjected to an initial freeze dryingstep at a primary drying pressure of 60 microns and at a shelftemperature of −30° C. for 60 hours; and subjecting the freeze-driedproduct to a secondary drying step at a drying pressure of 60 microns ata shelf temperature of +25° C. for 24 hours.

Anti-5T4 antibodies and antibody/drug conjugates are formulated in apharmaceutically acceptable carrier, for example, large slowlymetabolized macromolecules such as proteins, polypeptides, liposomes,polysaccharides, polylactic acids, polyglycolic acids, polymeric aminoacids, amino acid copolymers and inactive virus particles.Pharmaceutically acceptable salts may also be used, for example, mineralacid salts, such as hydrochlorides, hydrobromides, phosphates andsulfates, or salts of organic acids, such as acetates, propionates,malonates and benzoates. Formulations may additionally contain liquidssuch as water, saline, glycerol, and ethanol, and/or auxiliarysubstances, such as wetting or emulsifying agents or pH bufferingsubstances, may be present in such compositions. Such carriers enablethe compositions to be formulated as tablets, pills, dragees, capsules,liquids, gels, syrups, slurries and suspensions, for ingestion by thepatient.

V.E. Dose and Administration

Anti-5T4 antibodies and anti-5T4/drug conjugates of the invention may beadministered parenterally, for example, via intravascular, subcutaneous,intraperitoneal, or intramuscular administration. For delivery ofcompositions to pulmonary pathways, compositions may be administered asan aerosol or coarse spray, i.e. transnasal administration. Intrathecal,intra medullary, or intraventricular administration may be used fortreatment of central nervous system (CNS) cancers and CNS-relatedcancers. Anti-5T4 antibodies and anti-5T4/drug conjugates may also beadministered transdermally, transcutaneously, topically, enterally,intravaginally, sublingually or rectally. Intravenous administration maybe routinely used in the clinic. A delivery method is selected based onconsiderations such as the condition and site to be treated, the type ofantibody formulation, and the therapeutic efficacy of the composition.

The present invention provides that an effective amount of an anti-5T4antibody and anti-5T4/drug conjugate is administered to a subject, i.e.,an amount of an anti-5T4 antibody or anti-5T4/drug conjugate sufficientto elicit a desired biological response. For example, when administeredto a cancer-bearing subject, an effective amount comprises an amountsufficient to elicit anti-cancer activity, including cancer cellcytolysis, inhibition of cancer cell proliferation, induction of cancercell apoptosis, reduction of cancer cell antigens, delayed tumor growth,and/or inhibition of metastasis. Tumor shrinkage is well accepted as aclinical surrogate marker for efficacy. Another well accepted marker forefficacy is progression-free survival. Anti-5T4/calicheamicin conjugatesgenerally demonstrate at least a 25% improvement in key efficacyparameters, such as improvement in median survival, time to tumorprogression, and overall response rate.

Generally, an effective dose will be in the range from about 0.01 mg/m²to about 50 mg/m², such as from about 0.1 mg/m² to about 20 mg/m², orabout 15 mg/m², which dose is calculated based on the amount of anti-5T4antibody. An effective dose of an anti-5T4/drug conjugate may also becalculated based upon an amount of the conjugated drug. For example,representative doses of an anti-5T4/calicheamicin conjugate foradministration to experimental mouse models include 2 μg or 4 μgcalicheamicin, which may be scaled accordingly for administration tohumans. For example, anti-5T4/calicheamicin conjugates of the inventionmay be administered to human patients once every 3 weeks for up to 6cycles. For a radiolabeled anti-5T4 antibody, an effective dose istypically in the range from about 1 mCi to about 300 mCi, normally about5 mCi to 100 mCi, depending on the radioisotope and the binding affinityof the antibody.

For detection of 5T4-positive cells using the disclosed anti-5T4antibodies, a detectable amount of a composition of the invention isadministered to a subject, i.e., a dose of an anti-5T4 antibody suchthat the presence of the antibody may be determined in vitro or in vivo.For scintigraphic imaging using radioisotopes, typical doses of aradioisotope may include an activity of about 10 μCi to 50 mCi, or about100 μCi to 25 mCi, or about 500 μCi to 20 mCi, or about 1 mCi to 10 mCi,or about 10 mCi.

Actual dosage levels of active ingredients in a composition of theinvention may be varied so as to administer an amount of the compositionthat is effective to achieve the desired diagnostic or therapeuticoutcome. Administration regimens may also be varied. A single injectionor multiple injections may be used. The selected dosage level andregimen will depend upon a variety of factors including the activity andstability (i.e., half life) of the therapeutic composition, formulation,the route of administration, combination with other drugs or treatments,the disease or disorder to be detected and/or treated, and the physicalcondition and prior medical history of the subject being treated.

For anti-5T4 antibodies and anti-5T4/drug conjugates of the invention,the therapeutically effective dose may be estimated initially either incell culture assays or in animal models, such as rodents, rabbits, dogs,pigs, and/or or primates. The animal model may also be used to determinethe appropriate concentration range and route of administration. Suchinformation may then be used to determine useful doses and routes foradministration in humans. Typically, a minimal dose is administered, andthe dose is escalated in the absence of dose-limiting cytotoxicity.Determination and adjustment of an effective amount or dose, as well asevaluation of when and how to make such adjustments, are known to thoseof ordinary skill in the art of medicine.

For combination therapies, anti-5T4 antibodies, anti-5T4/drugconjugates, and/or additional therapeutic or diagnostic agents areadministered within any time frame suitable for performance of theintended therapy or diagnosis. Thus, the single agents may beadministered substantially simultaneously (i.e., as a single formulationor within minutes or hours) or consecutively in any order. For example,single agent treatments may be administered within about 1 year of eachother, such as within about 10, 8, 6, 4, or 2 months, or within 4, 3, 2or 1 week(s), or within about 5, 4, 3, 2 or 1 day(s).

For additional guidance regarding formulation, dose, administrationregimen, and measurable therapeutic outcomes, see Berkow et al. (2000)The Merck Manual of Medical Information, Merck & Co., Inc., WhitehouseStation, N.J.; Ebadi (1998) CRC Desk Reference of Clinical Pharmacology,CRC Press, Boca Raton, Fla.; Gennaro (2000) Remington: The Science andPractice of Pharmacy, Lippincott, Williams & Wilkins, Philadelphia, Pa.;Katzung (2001) Basic & Clinical Pharmacology, Lange MedicalBooks/McGraw-Hill Medical Pub. Div., New York; Hardman et al. (2001)Goodman & Gilman's the Pharmacological Basis of Therapeutics, TheMcGraw-Hill Companies, Columbus, Ohio; Speight & Holford (1997) Avery'sDrug Treatment: A Guide to the Properties, Choices, Therapeutic Use andEconomic Value of Drugs in Disease Management, Lippincott, Williams, &Wilkins, Philadelphia, Pa.

V.F. Combination Therapies

The disclosed anti-5T4 antibodies and anti-5T4/drug conjugates may beadministered as an initial treatment, or for treatment of conditionsthat are unresponsive to conventional therapies. In addition, theanti-5T4 antibodies and anti-5T4/drug conjugates may be used incombination with other therapies (e.g., surgical excision, radiation,additional anti-cancer drugs etc.) to thereby elicit additive orpotentiated therapeutic effects and/or reduce hepatocytotoxicity of someanti-cancer agents. Anti-5T4 antibodies and anti-5T4/drug conjugates ofthe invention may be co-administered or co-formulated with additionalagents, or formulated for consecutive administration with additionalagents in any order.

Representative agents useful for combination therapy include any of thedrugs described herein above as useful for preparation of anti-5T4/drugconjugates. Anti-5T4 antibodies and anti-5T4/drug conjugates of theinvention may also be used in combination with other therapeuticantibodies and antibody/drug conjugates, including anti-5T4 antibodiesother than the disclosed anti-5T4 antibodies, as well as antibodies andconjugates targeting a different antigen. Representative antibodies,which may be used alone or as an antibody/drug conjugate, includeanti-CD19 antibodies, anti-CD20 antibodies (e.g., RITUXAN®, ZEVALIN®,BEXXAR®), anti-CD22 antibodies, anti-CD33 antibodies (e.g., MYLOTARG®),anti-CD33 antibody/drug conjugates, anti-Lewis Y antibodies (e.g.,Hu3S193, Mthu3S193, AGmthu3S193), anti-HER-2 antibodies (e.g.,HERCEPTIN® (trastuzumab), MDX-210, OMNITARG® (pertuzumab, rhuMAb 2C4)),anti-CD52 antibodies (e.g., CAMPATH®), anti-EGFR antibodies (e.g.,ERBITUX® (cetuximab), ABX-EGF (panitumumab)), anti-VEGF antibodies(e.g., AVASTIN® (bevacizumab)), anti-DNA/histone complex antibodies(e.g., ch-TNT-1/b), anti-CEA antibodies (e.g., CEA-Cide, YMB-1003)hLM609, anti-CD47 antibodies (e.g., 6H9), anti-VEGFR2 (or kinase insertdomain-containing receptor, KDR) antibodies (e.g., IMC-1C11),anti-Ep-CAM antibodies (e.g., ING-1), anti-FAP antibodies (e.g.,sibrotuzumab), anti-DR4 antibodies (e.g., TRAIL-R), anti-progesteronereceptor antibodies (e.g., 2C5), anti-CA19.9 antibodies (e.g., GIVAREX®)and anti-fibrin antibodies (e.g., MH-1).

Anti-5T4 antibody/drug conjugates may also be administered together withone or more combinations of cytotoxic agents as part of a treatmentregimen. Useful cytotoxic preparations for this purpose include CHOPP(cyclophosphamide, doxorubicin, vincristine, prednisone andprocarbazine); CHOP (cyclophosphamide, doxorubicin, vincristine, andprednisone); COP (cyclophosphamide, vincristine, prednisone); CAP-BOP(cyclophosphamide, doxorubicin, procarbazine, bleomycin, vincristine andprednisone); m-BACOD (methotrexate, bleomycin, doxorubicin,cyclophosphamide, vincristine, dexamethasone, and leucovorin;ProMACE-MOPP (prednisone, methotrexate, doxorubicin, cyclophosphamide,etoposide, leukovorin, mechloethamine, vincristine, prednisone andprocarbazine); ProMACE-CytaBOM (prednisone, methotrexate, doxorubicin,cyclophosphamide, etoposide, leukovorin, cytarabine, bleomycin andvincristine); MACOP-B (methotrexate, doxorubicin, cyclophosphamide,vincristine, prednisone, bleomycin and leukovorin); MOPP(mechloethamine, vincristine, prednisone and procarbazine); ABVD(adriamycin/doxorubicin, bleomycin, vinblastine and dacarbazine); MOPP(mechloethamine, vincristine, prednisone and procarbazine) alternatingwith ABV (adriamycin/doxorubicin, bleomycin, vinblastine); MOPP(mechloethamine, vincristine, prednisone and procarbazin) alternatingwith ABVD (adriamycin/doxorubicin, bleomycin, vinblastine anddacarbazine); ChIVPP (chlorambucil, vinblastine, procarbazine,prednisone); IMVP-16 (ifosfamide, methotrexate, etoposide); MIME(methyl-gag, ifosfamide, methotrexate, etoposide); DHAP (dexamethasone,high-dose cytaribine and cisplatin); ESHAP (etoposide,methylpredisolone, HD cytarabine, and cisplatin); CEPP(B)(cyclophosphamide, etoposide, procarbazine, prednisone and bleomycin);CAMP (lomustine, mitoxantrone, cytarabine and prednisone); and CVP-1(cyclophosphamide, vincristine and prednisone); DHAP (cisplatin,high-dose cytarabine and dexamethasone); CAP (cyclophosphamide,doxorubicin, cisplatin); PV (cisplatin, vinblastine or vindesine); CE(carboplatin, etoposide); EP (etoposide, cisplatin); MVP (mitomycin,vinblastine or vindesine, cisplatin); PFL (cisplatin, 5-fluorouracil,leucovorin); IM (ifosfamide, mitomycin); IE (ifosfamide, etoposide); IP(ifosfamide, cisplatin); MIP (mitomycin, ifosfamide, cisplatin); ICE(ifosfamide, carboplatin, etoposide); PIE (cisplatin, ifosfamide,etoposide); Viorelbine and cisplatin; Carboplatin and paclitaxel; CAV(cyclophosphamide, doxorubicin, vincristine); CAE (cyclophosphamide,doxorubicin, etoposide); CAVE (cyclophosphamide, doxorubicin,vincristine, etoposide); EP (etoposide, cisplatin); and CMCcV(cyclophosphamide, methotrexate, lomustine, vincristine).

Anti-5T4 antibodies and anti-5T4/calicheamicin conjugates may be used incombination with systemic anti-cancer drugs, such as epithilones(BMS-247550, Epo-906), reformulations of taxanes (Abraxane, Xyotax),microtubulin inhibitors (MST-997, TTI-237), or with targeted cytotoxinssuch as CMD-193 and SGN-15. Additional useful anti-cancer agents includeTAXOTERE®, TARCEVA®, GEMZAR® (gemcitabine), 5-FU, AVASTIN®, ERBITUX®,TROVAX®, anatumomab mafenatox, letrazole, docetaxel, and anthracyclines.

For combination therapies, an anti-5T4 antibody, anti-5T4/drugconjugate, and/or one or more additional therapeutic or diagnosticagents are administered within any time frame suitable for performanceof the intended therapy or diagnosis. Thus, the single agents may beadministered substantially simultaneously (i.e., as a single formulationor within minutes or hours) or consecutively in any order. For example,single agent treatments may be administered within about 1 year of eachother, such as within about 10, 8, 6, 4, or 2 months, or within 4, 3, 2or 1 week(s), or within about 5, 4, 3, 2 or 1 day(s). The administrationof an anti-5T4 antibody or anti-5T4/calicheamicin conjugate incombination with a second therapeutic agent preferably elicits a greatereffect than administration of either alone.

EXAMPLES

The following examples have been included to illustrate modes of theinvention. Certain aspects of the following examples are described interms of techniques and procedures found or contemplated by the presentco-inventors to work well in the practice of the invention. Theseexamples illustrate standard laboratory practices of the co-inventors.In light of the present disclosure and the general level of skill in theart, those of skill will appreciate that the following examples areintended to be exemplary only and that numerous changes, modifications,and alterations may be employed without departing from the scope of theinvention.

Example 1 Murine Anti-5T4 Antibodies

Anti-5T4 antibodies were prepared in mice using human 5T4 antigen andstandard methods for immunization. Hybridoma cell lines producing theA1, A2, and A3 antibodies were produced by fusion of individual B cellswith myeloma cells.

The A1, A2, and A3 anti-5T4 antibody heavy chain and light chainvariable regions were cloned using the SMART® cDNA synthesis system(Clontech Laboratories Inc. of Mountain View, Calif.) followed by PCRamplification. The cDNA was synthesized from 1 μg total RNA isolatedfrom A1, A2, or A3 hybridoma cells, using oligo(dT) and the SMART® IIAoligo (Clontech Laboratories Inc.) with POWERSCRIPT™ reversetranscriptase (Clontech Laboratories Inc.). The cDNA was then amplifiedby PCR using a primer which anneals to the SMART® IIA oligo sequence andmouse constant region specific primer (mouse Kappa for the light chain,mouse IgG2a for the A1 heavy chain, mouse IgG2b for the A2 heavy chain,and mouse IgG1 for the A3 heavy chain) with VENT® polymerase (NewEngland Biolabs Inc. of Ipswich, Mass.). Heavy chain and light chainvariable region PCR products were subcloned into the pED6 expressionvector and the nucleic acid sequence was determined. This method isadvantageous in that no prior knowledge of the DNA sequence is required.In addition, the resultant DNA sequence is not altered by use ofdegenerate PCR primers.

The nucleotide sequences of the A1, A2, and A3 heavy chain variableregions are set forth as nucleotides 58-414 of SEQ ID NO:1, nucleotides55-405 of SEQ ID NO:5, and nucleotides 58-423 of SEQ ID NO:9,respectively. The amino acid sequences of the A1, A2, and A3 heavy chainvariable regions are set forth as residues 20-138 of SEQ ID NO:2,residues 19-135 of SEQ ID NO:6, and residues 20-141 of SEQ ID NO:10,respectively. The nucleotide sequences of the A1, A2, and A3 light chainvariable regions are set forth as nucleotides 61-381 of SEQ ID NO:3,nucleotides 67-390 of SEQ ID NO:7, and nucleotides 61-381 of SEQ IDNO:11, respectively. The amino acid sequences of the A1, A2, and A3light chain variable regions are set forth as residues 21-127 of SEQ IDNO:4, residues 23-130 of SEQ ID NO:8, and residues 21-127 of SEQ IDNO:12, respectively. See also FIGS. 1A-1C.

To assess the novelty of the A1, A2, and A3 anti-5T4 variable regionsequences, BLASTp searches (for protein query sequences) were conductedusing default parameters of Expect=10, Word Size=3, a low complexityfilter, and the BLOSUM62 matrix, permitting gap costs of existence=11,and extension=1. BLASTn searches (for nucleotide query sequences) wereconducted using default parameters of Expect=10, Word Size=11, and a lowcomplexity filter. BLAST search results are reported as a list ofsequences related to the query sequence, ranked in order of E value,which is an indicator of the statistical significance of matchesidentified in the database. Sequences most closely related to thevariable region sequences used for BLAST analysis are identified inTable 1 (BLASTn) and Table 2 (BLASTp).

TABLE 1 BLASTn Analysis Identity (%) of Query Closest Subject SequenceSequence Description of Closest Subject Sequence A1 VH 97%gi|31322165|gb|AY169686.1| Mus (SEQ ID NO: 1) musculus clone VGBC1.13immuno- globulin heavy chain variable region precursor, gene, partialcds A1 VL 96% gi|804922|dbj|D50385.1|MUSIKCVRJ (SEQ ID NO: 3) Musmusculus mRNA for immuno- globulin kappa chain variable region, partialsequence, cell_line: K3F10 A2 VH 97% gi|11612012|gb|AF303853.1|AF303853(SEQ ID NO: 5) Mus musculus clone J558.22 immuno- globulin heavy chainvariable region mRNA, partial cds A2 VL 97% gi|1556423|emb|X79906.1|(SEQ ID NO: 7) MMMABMST2 M. musculus mRNA for monoclonal antibody MST2light chain A3 VH 99% gi|3420272|gb|AF064445.1|AF064445 (SEQ ID NO: 9)Mus musculus immunoglobulin heavy chain variable region (Vh10.2) gene,Vh10.2a allele, partial cds A3 VL 98% gi|2906107|gb|AF045512.1|AF045512(SEQ ID Mus musculus 9E10 monoclonal antibody NO: 11) kappa light chainvariable region, (IgK) mRNA, partial cds

TABLE 2 BLASTp Analysis Identity (%) of Query Closest SubjectDescription of Closest Subject Sequence Sequence Sequence A1 VH 84%gi|15865327|emb|CAC82228.1| (SEQ ID NO: 2) immunoglobulin heavy chain[Mus musculus] A1 VL 93% gi|644862|gb|AAA62143.1| anti-alpha (SEQ ID NO:4) 4 integrin immunoglobulin kappa chain V region A2 VH 85%gi|15149453|gb|AAK85298.1| single (SEQ ID NO: 6) chain antibody HFN7.1[synthetic construct] A2 VL 95% gi|297678|emb|CAA80086.1| (SEQ ID NO: 8)immunoglobulin variable region [Mus musculus domesticus] A3 VH 90%gi|2906050|gb|AAC04511.1| (SEQ ID NO: 10) anti-poly(dC) monoclonalantibody heavy chain [Mus musculus] A3 VL 97% gi|2906108|gb|AAC04540.1|(SEQ ID NO: 12) monoclonal antibody kappa light chain [Mus musculus]

Example 2 Binding Specificity and Affinity of Murine Anti-5T4 Antibodies

To assess the binding specificity and affinity of the A1, A2, and A3antibodies, BIACORE® analysis was performed using human 5T4 antigenimmobilized on a CM5 chip. BIACORE® technology utilizes changes in therefractive index at the surface layer upon binding of the antibody tothe 5T4 antigen immobilized on the layer. Binding is detected by surfaceplasmon resonance (SPR) of laser light refracting from the surface.Analysis of the signal kinetics on rate and off rate allowsdiscrimination between non-specific and specific interactions. The H8anti-5T4 antibody was used as a control. H8 is a hybridoma-generatedmonoclonal mouse IgG1 antibody described in PCT InternationalPublication No. WO 98/55607 and in Forsberg et al. (1997) J. Biol. Chem.272(19):124430-12436.

TABLE 3 Results of BIACORE ® Assay Antibody KD (M) KA (1/M) kd (1/s) ka(1/Ms) H8 4.1 × 10⁻¹⁰ 2.5 × 10⁹ 5.1 × 10⁻⁵ 1.3 × 10⁵ A1 6.4 × 10⁻¹⁰ 1.6× 10⁹ 1.3 × 10⁻⁴ 2.0 × 10⁵ A2 1.5 × 10⁻⁸  6.5 × 10⁷ 8.7 × 10⁻⁴ 5.6 × 10⁴A3 2.2 × 10⁻⁹  4.6 × 10⁸ 5.2 × 10⁻⁵ 2.4 × 10⁴

The BIACORE® results show that H8 and A1 antibodies have higher affinityfor 5T4 when compared to the A2 and A3 antibodies. A2 is a relativelylow affinity antibody. Unusual cysteines are present at residue 67 ofthe A1 heavy chain variable region and residue 91 of the A3 heavy chainvariable region. Replacement of these residues with phenylalanine (A1)or tyrosine (A3) did not alter antibody binding properties or expressionlevels.

The binding affinity of the H8, A1, A2, and A3 antibodies was alsoassayed by Western blotting using CT26/5T4 cell lysates, whichidentified strong binding by H8, A1, and A3. See FIG. 2.

The ability of the H8, A1, A2, and A3 antibodies to bind cellsexpressing 5T4 antigen was assayed using fluorescence activated cellsorting (FACS) of PC14PE6 cells. All antibodies showed specific bindingto 5T4-expressing PC14PE6 cells, however, the level of A2 binding wassignificantly lower than that observed for H8, A1, and A3. See Table 4.

TABLE 4 Results of FACS Analysis Mean Cellular Antibody FlouresenceControl (secondary Ab) 4 Control (murine IgG) 4 H8 24 A1 18 A2 7 A3 27

To assess potential variability in antibody production, two independentpreparations of A1 and H8 were tested. The binding and kineticproperties of each antibody, when compared from each preparation, werenot significantly different. See FIGS. 3A-3B.

Example 3 Internalization of Murine Anti-5T4 Antibodies by5T4-Expressing Cells

To assess internalization of antibodies upon binding to 5T4 antigen, theamount of H8 and A1 antibodies detected at the cell surface versus inthe supernatant was determined as a function of time. Non-enzymaticallydissociated MDAMB435/5T4 cells (human breast cancer cells) were exposedto anti-5T4 antibodies for 1 hour at 4° C. Cells were washed andincubated in media at 37° C. for 4 hours or 24 hours. The amount ofantibody bound to cellular membranes versus unbound antibody (i.e.,presence in the supernatant) was determined using FACS. Thedisappearance of 5T4 antibodies from the surface of MDAMB435/5T4 cellsdemonstrates modulation of the 5T4 antigen/antibody complex at the cellsurface, which may indicate internalization and/or dissociation. SeeFIGS. 4A-4C.

Example 4 Epitope Mapping Using 5T4 Chimeras

To identify the epitopes to which each of the A1, A2, A3, and H8antibodies bind, ELISA assays were performed using (1) 5T4 ectodomain Fcconstructs with deleted or mutated sequences, and (2) 5T4 chimeraconstructs transiently expressed in COS-1 cells. The ectodomain includesthe amino-terminal region, two leucine-rich repeats, and the interveninghydrophilic region. Fusion proteins containing a 5T4 ectodomain and a Fcconstant regions from human IgG1 were prepared using mouse 5T4 (aminoacids 1-361), rat 5T4 (amino acids 1-361), cynomologous monkey 5T4(amino acids 1-355), chimpanzee 5T4 (amino acids 1-355), andblack-tailed marmoset (amino acids 1-355). The 5T4 chimera constructsare depicted in FIG. 5. The binding results are summarized in Table 5,which indicates specific binding, partial binding, or lack of binding,by each of the H8, A1, A2, and A3 antibodies. Humanized H8 and chimericA1, A2, and A3 antibodies showed binding properties similar to murineH8, A1, A2, and A3 respectively.

Based upon these results, it was determined that humanized H8 antibodybinds to human 5T4 between residues 173 and 252. Humanized H8 binds to5T4 with or without N-linked glycosylation at residue 344, whichconfirms that binding of humanized H8 to human 5T4 is not membraneproximal. The A1 antibody has a first contact with human 5T4 betweenresidues 173 and 252 and a second contact with human 5T4 betweenresidues 282 and 361. The A2 antibody binds human 5T4 between residues282 and 361. The A3 antibody binds the first leucine-rich repeat regionof human 5T4 between residues 83 through 163. The epitopes bound by eachantibody are depicted in FIG. 7.

TABLE 5 Results Epitope Mapping Using 5T4 Ectodomain Fc Fusions andHuman/Mouse 5T4 Chimeras Antibody 5T4 antigen construct H8 A1 A2 A3human 5T4 ectodomain Fc + + + + mouse 5T4 ectodomain Fc − − − − rat 5T4ectodomain Fc − +/− − − cynomologous monkey − + + + 5T4 ectodomain Fcchimpanzee 5T4 + + + + ectodomain Fc black-tailed marmoset 5T4 +/− + + −ectodomain Fc human/mouse 83-163 + + + − human/mouse 173-361 − − − +human/mouse 173-258 − +/− + + human/mouse 282-361 + +/− − + (with orwithout N-link at position 344) (+) binding; (−) no binding; (+/−)partial binding

Based upon the different binding observed to 5T4 ectodomains from humanand cynomologous monkey, targeted mutations were made to distinguishresidues that participate in antibody binding. Binding of humanized H8antibody was assayed to each of the mutated 5T4 ectodomains noted inTable 6 below, i.e., human 5T4 ectodomains that include a residue fromcynomologous monkey at the indicated position. These results showed thatresidues 213 and 214 of human 5T4 antigen are required for the epitopebound by humanized H8.

TABLE 6 Results of Epitope Mapping Using Human 5T4 Ectodomain/Fc FusionWith Targeted Mutations mutation humanized H8 binding E189K + V200K +L204V + R213H +/− R213H and R214L − (+) binding; (−) no binding; (+/−)partial binding

In addition to direct binding assays, competitive binding assays wereperformed using biotinylated humanized H8 antibody and each of the A1,A2, or A3 antibodies. Inhibition of binding to human 5T4 was notobserved, supporting that each of A1, A2, and A3 binds to a 5T4 epitopethat is distinct from that bound by the H8 antibody. See FIGS. 6A-6.

Example 5 Epitope Mapping Using BIACORE®

Epitope mapping of the H8, A1, A2, and A3 antibodies was also performedusing BIACORE® using a CM5 chip with bound human 5T4 antigen. The chipwas saturated with H8, A1, A2, or A3 antibody, and a first response wasmeasured. The chip was then saturated with a second antibody from amongthe H8, A1, A2, and A3 antibodies, and a second response was measured.For multiple experiments, the chip was regenerated by dissociation ofthe bound antibodies in 10 mM glycine, pH 1.5, followed by a bufferwash. The results are summarized in Table 7 below. The percentages shownare the response units measured upon binding by a second antibodydirectly to the CM5 chip divided by the response units measured uponbinding of the second antibody to a CM5 chip saturated with a firstantibody. These results show that H8, A1, A2, and A3 each bind adistinct epitope on human 5T4. The epitopes bound by the H8 and A3antibodies are sterically close to each other such that the rate ofassociation with antigen is decreased when binding of H8 is assayed inthe presence of A3, and vice versa. Similar results were obtained usingthe chimeric and humanized H8, A1, A2, and A3 antibodies, which wereprepared as described in Example 7 herein below. See Table 8.

TABLE 7 Results of Competition Assays Using BIACORE ® - PercentageResponse of Second Antibody Following Saturation With First Antibody1^(st) antibody 2nd antibody H8 A1 A2 A3 H8 — 114% 102% 85% A1 109%  —109% 98% A2 99%  98% — 94% A3 73% 104% 106% —

TABLE 8 Results of Competition Assays Using BIACORE ® - Percentage ofSecond Antibody Bound Following Saturation With First Antibody secondanti- body/first antibody time after injection of second antibody(seconds) bound 19 37.5 75 150 300 600 humanized H8/ 44.9% 57.0% 69.1%79.4% 86.6% 91.3% chimeric A3 chimeric A3/ 46.2% 51.2% 58.4% 67.5% 76.2%83.6% humanized H8 chimeric A2/ 102.9% 93.5% 90.1% 89.0% 88.9% 89.1%chimeric A1 chimeric A1/ 92.5% 90.6% 91.4% 92.7% 93.9% 95.5% chimeric A2chimeric A3/ 82.1% 82.0% 84.5% 87.8% 90.8% 92.8% chimeric A1 chimericA1/ 98.8% 96.5% 97.0% 98.0% 98.8% 99.6% chimeric A3 chimeric A3/ 92.2%88.6% 89.5% 91.5% 93.4% 94.6% chimeric A2 chimeric A2/ 89.2% 88.4% 89.8%91.5% 92.9% 94.3% chimeric A3 humanized H8/ 93.2% 92.7% 94.2% 95.9%96.9% 97.3% chimeric A1 chimeric A1/ 92.7% 92.4% 93.8% 95.8% 97.3% 98.7%humanized H8 humanized H8/ 93.8% 94.0% 96.0% 98.1% 99.8% 101.3% chimericA2 chimeric A2/ 86.9% 84.7% 86.9% 90.5% 93.7% 96.7% humanized H8

The combined results of epitope mapping studies as determined usingchimeric constructs (see Example 4) and BIACORE® are presented in FIG.7.

Example 6 Efficacy of Anti-5T4/Calicheamicin Conjugates

A vital dye (MTS) staining was used to determine the number of survivingcells following exposure to various treatments. MTS (non-radioactivecell proliferation assay kit) was purchased from Promega (Madison, Wis.)and used according to the manufacturer's specifications. For each cellline a calibration curve (cell number versus optical density after 2hours) was established to estimate an appropriate initial seedingdensity. Cells were then seeded in 96-multiwell dishes at a density of750 to 5,000 cells per well. Immediately after seeding, the cells wereexposed to various concentrations (0, 0.01, 0.05, 0.1, 1, 10, 100 and500 ng calicheamicin equivalents/ml) of calicheamicin, CMA-676 andcalicheamicin conjugates of anti-5T4 antibodies. Following determinationof the number of cells surviving 96 hours of drug-exposure, the ED₅₀ wascalculated based on the logistic regression parameters derived from thedose-response curves. The ED₅₀ was defined as the concentration of drug(CalichDMH) that caused a 50% reduction of the cell number after 96hours exposure to the drug. A calicheamicin equivalent (cal. eq.) is theconcentration of calicheamicin given either as a pure substance or as aconjugate. Depending on the amount of calicheamicin bound to theantibody (antibody drug loading), calicheamicin equivalents which aredifferent may indicate different protein concentrations.

The results of MTS assays are shown in Table 9. Antibody/calicheamicinconjugates prepared using the A1 and A3 anti-5T4 assays substantiallyreduced viability of MDAMB435/5T4 cells. Selectivity values werecalculated by comparing the specific activity of the conjugate to thenon-specific activity. That is, fold CalichDMH for the 5T4 expressingcells were divided by the fold CalichDMN values for cells not expressing5T4. When a non-specific antibody is used, for example hp67.6 (CMA-676),the fold CalichDMH values are approximately the same such that theselectivity is 1.

TABLE 9 Results of MTS Assays cell line MDAMB435/neo MDAMB435/5T4Treatment ED50 (ng/ml) ED50 (ng/ml) CalichDMH 3.3-5.0 5.0-8.0huH8-ActBut-CalichDMH 0.4-0.8 0.08-0.1  CMA-676 34-60  50-100A1-ActBut-CalichDMH 22-34 0.4-0.6 A2-ActBut-CalichDMH 60 40A3-ActBut-CalichDMH 20-20 0.3-20  cell line MDAMB435/neo MDAMB435/5T4treatment Fold CalichDMH Fold CalichDMH CalichDMH 1.0-1.0 1.0-1.0huH8-ActBut-CalichDMH  4.0-12.5  50-100 CMA-676 0.08-0.1  0.08-0.1 A1-ActBut-CalichDMH 0.14-0.15 13-13 A2-ActBut-CalichDMH 0.06 0.13A3-ActBut-CalichDMH 0.17-0.25 0.4-17  Selectivity: H8 = 8; hP67.6 = 1;A1 = 93; A3 = 1.6 CalichDMH, unconjugated calicheamicinhuH8-AcBut-CalichDMH, humanized H8 antibody conjugated to calicheamicinusing 4-(4′-acetylphenoxy)butanoic acid (AcBut) CMA-676,anti-CD33/calicheamicin conjugate A1-AcBut-CalichDMH, A1 antibodyconjugated to calicheamicin using 4-(4′-acetylphenoxy)butanoic acid(AcBut) A2-AcBut-CalichDMH, A2 antibody conjugated to calicheamicinusing 4-(4′-acetylphenoxy)butanoic acid (AcBut) A3-AcBut-CalichDMH, A3antibody conjugated to calicheamicin using 4-(4′-acetylphenoxy)butanoicacid (AcBut)

The cytotoxicity of anti-5T4/calicheamicin conjugates was also assayedusing a three-dimensional spheroid cell culture that more closelyapproximates an in vivo cellular environment. Spheroids were madeessentially according to Yuhas et al. (1977) Cancer Res. 37:3639-3643.Briefly, 10⁵ cells in 5 ml of culture medium were seeded on 60 mmpolystyrene cell culture dishes previously coated with 5 ml 0.65% tissueculture grade agar in culture medium (Sigma of St. Louis, Mo.). Thedishes were incubated for 5-6 days at 37° C. and in 5% CO₂ in air.Spheroids with a diameter of 0.2 mm were selected and placed in a24-well multiwell dish. Each well contained 0.5 ml agar underlay, 1spheroid, and 1 ml culture medium overlay. The spheroids were thenexposed to various concentrations (0, 0.091, 0.365, 1.46, 5.86, 23.44,93.75 and 375 ng calicheamicin equivalents/ml) of calicheamicin, CMA-676and anti-5T4/calicheamicin conjugates prepared using the A1 and A3anti-5T4 antibodies and an AcBut linker. Both anti-5T4/calicheamicinconjugates significantly inhibited growth of MDAMB435/5T4 cells. SeeFIG. 8.

Example 7 Preparation and Binding Properties of Chimeric and HumanizedAnti-5T4 Antibodies

Chimeric H8, A1, A2, and A3 antibodies were constructed having murine H8heavy chain and light chain variable regions sequences and human IgG4heavy chain constant regions and human kappa light chain constantregions. The cysteine present at position 67 of the A1 heavy chainvariable region was optionally changed to phenylalanine, and thecysteine present at position 91 of the A3 heavy chain variable regionwas optionally changed to tyrosine. These variants are set for in SEQ IDNO:2 (A1 VH) and SEQ ID NO:10 (A3 VH). The presence or absence ofintronic sequences and the replacement of cysteine residues did notaffect antibody expression. For cloning of sequences encoding IgGconstant regions, intronic sequences were optionally deleted.

Humanized H8 was prepared as described in PCT International PublicationNo. WO 2006/031653. Humanized A1 antibodies were prepared by CDRgrafting as described further herein below. The CDRs of the murine A1,A2, and A3 antibodies were identified using the AbM definition, which isbased on sequence variability as well as the location of the structuralloop regions. In general, human acceptor frameworks were selected on thebasis that they are substantially similar to the framework regions ofthe murine antibodies, or which were most similar to the consensussequence of the variable region subfamily. Consideration was also givento representation of the framework loci in humans, such that widelyrepresented sequences were generally preferred over less populoussequences. Additional mutations of the human framework acceptorsequences were made to restore murine residues believed to be involvedin antigen contacts and/or residues involved in the structural integrityof the antigen-binding site. The amino acid sequence may also beoptimized for codon preference of CHO cells and to remove restrictionenzyme sites. A peptide structure prediction program may be used toanalyze the humanized variable heavy and light region sequences toidentify and avoid post-translational protein modification sitesintroduced by the humanization design.

A humanized A1 heavy chain variable region (A1 VH version 1.0) wasconstructed to include the CDRs of murine A1 grafted onto a human DP-21framework region (VH7 subgroup, Accession No. CAA43346, SEQ ID NO:88),which contains a framework mutation (S82A) and one backmutation (E46K).Variants were prepared by removing the backmutation (A1 VH versions 1.1and 1.2). A second humanized A1 heavy chain variable region was preparedby grafting A1 CDRs onto a human DP-54 germline framework region (A1 VHversion 2.0). Six (6) backmutations were made to produce A1 VH version2.1. As described further below, both A1 heavy chain variable regionsretained 5T4 binding properties. The DP-21 and DP-54 framework regionsshow 63% amino acid sequence identity over their length, indicating thatnumerous amino acid changes may be made to while preserving the bindingspecificity of the antibody, including the ability to bind to aparticular epitope. The similarity of humanized A1 heavy chain variableregions is shown in Table 10. Representative nucleotide sequencesencoding humanized A1 heavy chain variable regions are set forth as SEQID NOs:48, 50, 53, and 55. Representative amino acid sequences ofhumanized A1 heavy chain variable regions are set forth as SEQ IDNOs:49, 51, 52, 54, and 56. See also FIGS. 9A-9B.

A humanized A1 light chain variable region was constructed to includethe CDRs of murine A1 grafted onto human DPK24 (VKIV subgroup), DPK9(VKI subgroup), and DPK23 (VKIII subgroup) germline framework regions.After incorporation of a S67Y backmutation into humanized A1 light chainvariable region frameworks prepared with each of these frameworksdemonstrated 5T4 binding. See below, including Table 13. The DPK24framework region shows 74% and 73% amino acid sequence identity over itslength to DPK9 and DPK23, respectively. The DPK9 framework region shows74% amino acid sequence identity over its length to DPK23. Thesimilarity of humanized A1 light chain variable regions is shown inTable 10. The multiple versions of humanized light chain variableframework regions demonstrate that numerous amino acid changes may bemade to while preserving the binding specificity of the antibody,including the ability to bind to a particular epitope. Representativenucleotide sequences encoding humanized A1 light chain variable regionsare set forth as SEQ ID NOs:57, 59, 61, 63, 65, 67, 69, 71, 73, and 75.Representative amino acid sequences of humanized A1 light chain variableregions are set forth as SEQ ID NOs:58, 60, 62, 64, 66, 68, 70, 72, 74,and 76. See also FIGS. 9C-9F.

TABLE 10 Relatedness of Humanized A1 Antibodies 1^(st) VariableRegion/2^(nd) Variable Region Percentage Identity HuA1 VL v1.1 (SEQ IDNO: 60)/ 86% HuA1 VL v2.4 protein (SEQ ID NO: 70) HuA1 VL v1.1 (SEQ IDNO: 60)/ 86% HuA1 VL v3.1 protein (SEQ ID NO: 75) HuA1 VL v2.4 protein(SEQ ID NO: 70)/ 85% HuA1 VL v3.1 protein (SEQ ID NO: 75) HuA1 VH v1.1protein (SEQ ID NO: 52)/ 78% HuA1 VH v2.0 protein (SEQ ID NO: 54)

Humanized A2 and A3 antibodies were designed using a similar strategy.Representative amino acid sequences of humanized A2 heavy chain variableregions and humanized A2 light chain variable regions are set forth asSEQ ID NOs:77-78 and SEQ ID NOs:79-80, respectively. See also FIG. 9G.Representative amino acid sequences of humanized A3 heavy chain variableregions and humanized A3 light chain variable regions are set forth asSEQ ID NOs:81-82 and SEQ ID NOs:83-84, respectively. See also FIG. 9H.

To assess the novelty of humanized A1, A2, and A3 heavy chain and lightchain variable regions, BLASTn and BLASTp analysis was performed asdescribed in Example 1. The results are presented in Table 11.

TABLE 11 BLASTn and BLASTp Analysis Identity (%) of Closest QuerySequence Subject Sequence Description of Closest Subject SequenceHumanized A1 VL  83%* DEFINITION Homo sapiens partial mRNA forimmunoglobulin version 1.1 DNA kappa chain variable region (IGKV2 gene).(SEQ ID NO: 59) ACCESSION AM040532 Humanized A1 VL 82% DEFINITION Igkappa chain V-IV region B17 precursor. version 1.1 protein ACCESSIONP06314 (SEQ ID NO: 60) Humanized A1 VL  85%* DEFINITION Homo sapiensclone SC4064 anti-rabies virus version 2.4 DNA immunoglobulin lightchain variable region mRNA, complete (SEQ ID NO: 69) cds. ACCESSIONAY942044 Humanized A1 VL 92% DEFINITION anti-alpha 4 integrin humanizedimmunoglobulin version 2.4 protein kappa chain V region. (SEQ ID NO: 70)ACCESSION AAA62146 Humanized A1 VL  84%* DEFINITION Homo sapiens clone136e06 anti-tetanus toxoid version 3.1 DNA immunoglobulin light chainvariable region (IGL@) mRNA, (SEQ ID NO: 75) partial cds. ACCESSIONAY867377 Humanized A1 VL 84% DEFINITION anti-Burkholderia mallei scFvantibody [synthetic version 3.1 protein construct]. (SEQ ID NO: 76)ACCESSION ABI97018 Humanized A1 VH  88%* DEFINITION Homo sapiens ID:CLL097 IgA heavy chain version 1.1 DNA variable region mRNA, partialcds. (SEQ ID NO: 50) ACCESSION AF021940 Humanized A1 VH 90% DEFINITIONIgA heavy chain variable region [Homo sapiens]. version 1.1 proteinACCESSION AAC09074 (SEQ ID NO: 51) Humanized A1 VH  81%* DEFINITION Homosapiens clone 23u-45 immunoglobulin version 2.0 DNA heavy chain variableregion (IGH) mRNA, partial cds. (SEQ ID NO: 53) ACCESSION AF062241Humanized A1 VH 77% DEFINITION Chain D, Insights Into Erbb SignalingFrom The version 2.0 protein Structure Of The Erbb2-Pertuzumab Complex.(SEQ ID NO: 54) ACCESSION 1S78_D Humanized A2 VL 87% DEFINITION Chain A,Crystal Structure Of The Fab Fragment version 1.0 protein Of A HumanMonoclonal Igm Cold Agglutinin. (SEQ ID NO: 79) ACCESSION 1QLR_AHumanized A2 VL 83% DEFINITION kappa 1 immunoglobulin light chain [Homoversion 2.0 protein sapiens]. (SEQ ID NO: 80) ACCESSION AAD29608Humanized A2 VH 88% DEFINITION Chain A, The Crystal Structure Of AHumanized version 1.0 protein Antibody Fv 528. (SEQ ID NO: 77) ACCESSION1WT5_A Humanized A2 VH 78% DEFINITION Chain D, Insights Into ErbbSignaling From The version 2.0 protein Structure Of The Erbb2-PertuzumabComplex. (SEQ ID NO: 78) ACCESSION 1S78_D Humanized A3 VL 85% DEFINITIONimmunoglobulin kappa light chain VLJ region version 1.0 protein [Homosapiens]. (SEQ ID NO: 83) ACCESSION BAC01708 Humanized A3 VL 90%DEFINITION HerMel [synthetic construct]. version 2.0 protein ACCESSIONCAL47329 (SEQ ID NO: 84) Humanized A3 VH 79% DEFINITION Igh-1a protein[Mus musculus]. version 1.0 protein ACCESSION AAH80671 (SEQ ID NO: 81)Humanized A3 VH 77% DEFINITION Igh-1a protein [Mus musculus]. version2.0 protein ACCESSION AAH80671 (SEQ ID NO: 82) *When Query Coverage =100%

FIGS. 10A-10B show additional heavy chain variable region sequences thatmay be used as frameworks for preparation of humanized A1, A2, and A3anti-5T4 antibodies. FIGS. 11-13 show additional light chain variableregion sequences that may be used as a framework for preparation ofhumanized A1, A2, and A3 anti-5T4 antibodies. FIG. 14 showsrepresentative constant regions that may be used for the preparation ofchimeric and humanized A1, A2, and A3 anti-5T4 antibodies.

To assess the binding specificity and affinity of the chimeric andhumanized H8, A1, A2, and A3 antibodies, BIACORE® analysis was performedusing human 5T4 antigen immobilized on a CM5 chip. See Example 2. Theresults for chimeric A1, A2, and A3 antibodies are shown in Table 12below.

TABLE 12 Results of BIACORE ® Assay Antibody KD (M) KA (1/M) kd (1/s) ka(1/Ms) Humanized H8 1.5 × 10⁻¹⁰ 6.5 × 10⁹ 4.0 × 10⁻⁵ 2.6 × 10⁵ ChimericA1 4.4 × 10⁻¹⁰ 2.3 × 10⁹ 6.7 × 10⁻⁵ 1.5 × 10⁵ Chimeric A2 1.8 × 10⁻⁹ 5.7 × 10⁸ 2.5 × 10⁻⁴ 1.4 × 10⁵ Chimeric A3 ~1.8 × 10⁻¹⁰  ~5.4 × 10⁹ ~1.0 × 10⁻⁵  ~5.4 × 10⁴  Chimeric A1 + C67F 3.8 × 10⁻¹⁰ 2.6 × 10⁹ 6.3 ×10⁻⁵ 1.7 × 10⁵ Chimeric A3 + C91Y 5.9 × 10⁻⁹  1.7 × 10⁹ 1.6 × 10⁻⁵ 2.7 ×10⁴

In general, chimerization/humanization increased the affinity of H8, A1,A2, and A3 to human 5T4. Compare Table 3. The increase in bindingaffinities appears to result primarily from a slower dissociation of theantibody and antigen rather than a faster association. The chimeric A2and A3 antibodies showed the most improved binding properties followingchimerization.

All humanized A1 heavy chain variable regions retained 5T4 bindingproperties. In addition, removal of the K46 backmutation from humanizedA1 heavy chain variable region did not affect 5T4 binding properties.Humanized A1 light chain variable regions showed compromised 5T4 bindingproperties. Humanized A1 light chain variable regions constructed usingDPK9 and DPK23 frameworks bound 5T4 with higher affinity than ahumanized A1 light chain variable regions constructed using DPK24frameworks. Backmutations were incorporated to restore and/or optimize5T4 binding. Replacement of the serine residue at position 67 with atyrosine residue, as seen in the murine A1 framework region, completelyrestored 5T4 antigen binding properties. See Table 13.

TABLE 13 Inhibition of Biotinylated Chimeric A1 Antibody Binding toHuman 5T4 by ELISA Version A1 Antibody IC₅₀ Chimeric A1 16-20 nM huA1V_(H) v2.0 + huA1 V_(L) v1.1 >1 μM huA1 V_(H) v2.0 + huA1 V_(L) v1.1 28nM huA1 V_(H) v2.0 + huA1 V_(L) v2.0 >1 μM huA1 V_(H) v2.0 + huA1 V_(L)v2.4 16 nM huA1 V_(H) v2.0 + huA1 V_(L) v3.0 >1 μM huA1 V_(H) v2.0 +huA1 V_(L) v3.1 27 nM huA1, humanized A1 v, version

Example 8 Species Cross-Reactivity of Anti-5T4 Antibodies

The cross-species reactivity of anti-5T4 antibodies disclosed herein wasassayed to determine relevant species for in vivo efficacy studies andtoxicology analysis. Correlation of binding activity and relatedness ofthe different 5T4 ectodomains was also used to further describe theepitope bound by each antibody. Binding assays were performed using 5T4ectodomains from various species fused to human IgG1 Fc. The percentageidentity of each ectodomain region to human 5T4 is shown in Table 14.

TABLE 14 Relatedness of 5T4 From Different Species Percentage IdentityAmino Acids Species to Human 5T4 of Ectodomain Human 100 1-355 Mouse84.0  1-361 ^(a) Rat 83.1  1-361 ^(a) Chimpanzee ~99.5 1-355 (partialsequence - 396/420 amino acids) Cynomologous Monkey 96.7 1-355Black-Tailed Marmoset ~94.6 1-355 (partial sequence - 367/420 aminoacids) Dog 87.9 1-355 Cow 86.9 1-355 ^(a) Contains 6 amino acid directrepeat within hydrophilic domain

The full-length or partial sequences of 5T4 from human, mouse, rat, dog,and cow have been disclosed previously as GenBank Accession Nos. Z29083(human, SEQ ID NO:87), AJ012160 (mouse), BC087011 (rat), XM539020 (dog),and XM593502 (cow). A virtual partial sequence of chimpanzee 5T4 wasgenerated using an alignment of mRNA and genomic sequences. Nucleicacids encoding 5T4 proteins were isolated from cynomologous monkey andblack-tailed marmoset. The amino acid sequences of these additional 5T4antigens are shown in FIG. 15 and are also set forth as SEQ ID NO:86(cynomologous monkey) and SEQ ID NO:85 (black-tailed marmoset).

To assess the novelty of cynomologous monkey and black-tailed marmosetsequences, BLAST analyses were performed as described in Example 2. Whenusing the full-length black-tailed marmoset 5T4 amino acid sequence as aquery sequence, the closest subject sequence was identified as human 5T4(GenBank Accession No. NP_(—)006661.1), with 94% identity (302/320 aminoacids). The sequences also differed at the carboxyl terminus, with aminoacids 1-19 of SEQ ID NO:85 not aligning with the closest subjectsequence. When using the full-length cynomologous monkey 5T4 amino acidsequence as a query sequence, the closest non-virtual subject sequencewas identified as a trophoblast glycoprotein precursor also fromcynomologous monkey (GenBank Accession No. BAE00432.1), with 99%identity (364/366 amino acids). The sequences also differed at thecarboxyl terminus, with amino acids 1-25 of SEQ ID NO:86 not aligningwith the closest non-virtual subject sequence.

To assay binding of anti-5T4 antibodies, 5T4 ectodomain/Fc fusionproteins were transiently transfected into COS-1 cells, and ELISA assayswere performed. Non-relevant human IgG4 and IgG1 antibodies were used ascontrols. The cross-species reactivity of anti-5T4 antibodies issummarized in Table 15.

TABLE 15 Cross-Reactivity of Anti-5T4 Antibodies (ED50 in nM) huH8 huH8ChiA1 ChiA2 ChiA3 γ4 γ1 γ4 γ4 γ4 human 0.19 0.20 0.28 0.21 0.20chimpanzee 0.19 0.22 0.27 0.22 0.20 black-tailed +/− +/− 0.24 0.22 −marmoset cynomologous − − 0.18 0.18 0.23 monkey rat − − +/− − − mouse −− − − − huH8 γ4, humanized H8 antibody having IgG4 constant regions huH8γ1, humanized H8 antibody having IgG1 constant regions ChiA1 γ4,chimeric A1 antibody having IgG4 constant regions ChiA2 γ4, chimeric A2antibody having IgG4 constant regions ChiA3 γ4, chimeric A3 antibodyhaving IgG4 constant regions (+/−), partial binding (−), no binding

1. An isolated antibody, or fragment thereof, that specifically bindshuman 5T4 antigen, wherein the antibody or antibody fragment comprisesan antigen binding domain of, competes for 5T4 binding with, or binds a5T4 epitope bound by, an antibody comprising a heavy chain variableregion having an amino acid sequence set forth as SEQ ID NO:2 and alight chain variable region having an amino acid sequence set forth asSEQ ID NO:4.
 2. The antibody of claim 1, which is a chimeric antibody, ahumanized antibody, a single chain antibody, a Fab fragment, a F(ab)₂fragment, a Fv fragment, a tetrameric antibody, a tetravalent antibody,a multispecific antibody, or a fusion protein.
 3. The antibody of claim1, which is a murine monoclonal antibody.
 4. The antibody of claim 1,which has a binding affinity for human 5T4 antigen of at least about1×10⁻⁷ to about 1×10⁻¹² M.
 5. The antibody of claim 1, whichspecifically targets 5T4-expressing cells in vivo.
 6. The antibody ofclaim 3, wherein the murine monoclonal antibody comprises a heavy chainvariable region comprising an amino acid sequence of residues 20-138 ofSEQ ID NO:2.
 7. The antibody of claim 3, wherein the murine monoclonalantibody comprises a light chain variable region comprising an aminoacid sequence of residues 21-127 of SEQ ID NO:4.
 8. The antibody ofclaim 3, wherein the murine monoclonal antibody comprises a heavy chainvariable region comprising an amino acid sequence of residues 20-138 ofSEQ ID NO:2, and wherein the light chain variable region of the murinemonoclonal antibody comprises an amino acid sequence of residues 21-127of SEQ ID NO:4.
 9. The antibody of claim 2, which is a chimeric orhumanized anti-5T4 antibody.
 10. The chimeric or humanized antibody ofclaim 9, which comprises human constant regions.
 11. The chimeric orhumanized antibody of claim 10, which comprises a human kappa lightchain constant region.
 12. The chimeric or humanized antibody of claim10, which comprises a human IgG1, IgG2, IgG3, or IgG4 heavy chainconstant region.
 13. The chimeric or humanized antibody of claim 12,wherein the human IgG4 heavy chain constant region comprises proline atposition
 241. 14. The humanized antibody of claim 9, which comprises atleast one light chain variable region and at least one heavy chainvariable region comprising, framework regions comprising human residuesof a human antibody framework region; and wherein the at least one lightchain variable region comprises three CDRs of SEQ ID NO:4.
 15. Thehumanized antibody of claim 14, wherein the human residues are humanframework residues selected from the group consisting of: (a) a humanantibody heavy chain framework region of any one of SEQ ID NOs:14-23,77, and 88-93; (b) a human antibody light chain framework region of anyone of SEQ ID NOs:28-34, 35-44, and 94-99; (c) a consensus sequence of aheavy chain framework region of (a); and (d) a framework region that isat least 63% identical to a framework region of (a)-(c).
 16. Thehumanized antibody of claim 14, wherein the at least one heavy chain ofthe humanized antibody comprises a variable region comprising three CDRsof SEQ ID NO:2.
 17. The chimeric or humanized antibody of claim 9, whichcomprises a heavy chain variable region sequence comprising: (a) anamino acid sequence of residues 20-138 of SEQ ID NO:2; or (b) an aminoacid sequence of any one of SEQ ID NOs:49, 51, 52, 54, or
 56. 18. Thechimeric or humanized antibody of claim 9, which comprises a light chainvariable region sequence comprising: (a) an amino acid sequence ofresidues 21-127 of SEQ ID NO:4; or (b) an amino acid sequence of any oneof SEQ ID NOs: 58, 60, 62, 64, 66, 68, 70, 72, 74, or
 76. 19. Anantibody/drug conjugate for drug delivery comprising: (a) an antibodyaccording to claim 1; and (b) a drug, which is directly or indirectlybound to the antibody.
 20. The antibody/drug conjugate of claim 19,wherein the drug is a therapeutic agent selected from the groupconsisting of a cytotoxin, a radioisotope, an immunomodulatory agent, ananti-angiogenic agent, an anti-proliferative agent, a pro-apoptoticagent, a chemotherapeutic agent, and a therapeutic nucleic acid.
 21. Theantibody/drug conjugate of claim 20, wherein the therapeutic agent is acytotoxin.
 22. The antibody/drug conjugate of claim 20, wherein thecytotoxin is an antibiotic, an inhibitor of tubulin polymerization, analkylating agent, a protein synthesis inhibitor, a protein kinaseinhibitor, a phosphatase inhibitor, a topoisomerase inhibitor, or anenzyme.
 23. The antibody/drug conjugate of claim 20, wherein thecytotoxin is an antibiotic.
 24. The antibody/drug conjugate of claim 23,wherein the antibiotic is calicheamicin.
 25. The antibody/drug conjugateof claim 24, wherein the calicheamicin is an N-acetyl derivative ordisulfide analog of calicheamicin.
 26. The antibody/drug conjugate ofclaim 25, wherein the calicheamicin is N-acetyl-γ-calicheamicin.
 27. Theantibody/drug conjugate of claim 19, wherein the drug is bound to theantibody via a linker.
 28. The antibody/drug conjugate of claim 27,wherein the linker is selected from the group consisting of4-(4′acetylphenoxy)butanoic acid (AcBut), 3-acetylphenyl acidic acid(AcPac), 4-mercapto-4-methyl-pentanoic acid (Amide), and derivativesthereof.
 29. An isolated antibody that specifically binds to a human 5T4epitope comprising residues 173-252 and 276-355 of SEQ ID NO:87.
 30. Thechimeric or humanized antibody of claim 9, which comprises: (a) a lightchain variable region comprising an amino acid sequence selected fromthe group consisting of an amino acid sequence of residues 21-127 of SEQID NO:4 and any one of SEQ ID NOs: 58, 60, 62, 64, 66, 68, 70, 72, 74,or 76; and (a) a heavy chain variable region comprising an amino acidsequence selected from the group consisting of residues 20-138 of SEQ IDNO:2and any one of SEQ ID NOs:49, 51, 52, 54, or
 56. 31. The chimeric orhumanized antibody of claim 9, which comprises: (a) a light chainvariable region comprising an amino acid sequence of SEQ ID NO: 70; and(a) a heavy chain variable region comprising an amino acid sequence ofSEQ ID NO: 54.